{"id":2515,"date":"2026-05-28T17:13:55","date_gmt":"2026-05-28T11:43:55","guid":{"rendered":"https:\/\/mymockmate.com\/notes\/?p=2515"},"modified":"2026-06-18T12:02:14","modified_gmt":"2026-06-18T06:32:14","slug":"ncert-class-9-science-journey-inside-the-atom-question-answers","status":"publish","type":"post","link":"https:\/\/mymockmate.com\/notes\/ncert-class-9-science-journey-inside-the-atom-question-answers\/","title":{"rendered":"NCERT  Class 9 Science Journey Inside the Atom  Question Answers"},"content":{"rendered":"<div class=\"mymoc-top mymoc-entity-placement\" id=\"mymoc-619059811\"><div id=\"mymoc-2189055347\"><a href=\"https:\/\/amzn.to\/4xnw9oY\" aria-label=\"head-phones\"><img src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/head-phones.png\" alt=\"\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/head-phones.png 1301w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/head-phones-300x80.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/head-phones-1024x274.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/head-phones-768x205.png 768w\" sizes=\"(max-width: 1301px) 100vw, 1301px\" width=\"1301\" height=\"348\"><\/a><\/div><\/div><div class=\"pdfprnt-buttons pdfprnt-buttons-post pdfprnt-top-bottom-right\"><a href=\"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/posts\/2515?print=print\" class=\"pdfprnt-button pdfprnt-button-print\" target=\"_blank\"><img decoding=\"async\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/plugins\/pdf-print\/images\/print.png\" alt=\"image_print\" title=\"Print Content\"><span class=\"pdfprnt-button-title pdfprnt-button-print-title\">Print<\/span><\/a> <span class=\"pdfprnt-count-generation\">16<\/span><\/div>\n<h1 class=\"wp-block-heading\">Short Intro<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">This chapter explains the fascinating journey of discovering the structure of the atom. Students learn about atomic models proposed by Dalton, Thomson, Rutherford, and Bohr along with concepts such as atomic number, mass number, isotopes, isobars, electronic configuration, and valency.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">Quick Information Box<\/h1>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Topic<\/th><th>Details<\/th><\/tr><\/thead><tbody><tr><td>Chapter Name<\/td><td>Journey Inside the Atom<\/td><\/tr><tr><td>Class<\/td><td>Grade 9<\/td><\/tr><tr><td>Subject<\/td><td>Science<\/td><\/tr><tr><td>Main Concepts<\/td><td>Atomic Models, Electrons, Protons, Neutrons<\/td><\/tr><tr><td>Important Scientist<\/td><td>Rutherford, Bohr, Chadwick<\/td><\/tr><tr><td>Key Formula<\/td><td>Mass Number = Protons + Neutrons<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h1 class=\"wp-block-heading\">Concepts Used (Topics Covered)<\/h1>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Dalton&rsquo;s Atomic Theory<\/li>\n\n\n\n<li>Thomson&rsquo;s Plum Pudding Model<\/li>\n\n\n\n<li>Rutherford&rsquo;s Gold Foil Experiment<\/li>\n\n\n\n<li>Bohr&rsquo;s Atomic Model<\/li>\n\n\n\n<li>Discovery of Electron, Proton and Neutron<\/li>\n\n\n\n<li>Atomic Number and Mass Number<\/li>\n\n\n\n<li>Electronic Configuration<\/li>\n\n\n\n<li>Valency<\/li>\n\n\n\n<li>Isotopes and Isobars<\/li>\n\n\n\n<li>Average Atomic Mass<\/li>\n<\/ul>\n\n\n\n<h1 class=\"wp-block-heading\">Important Formulas<\/h1>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Atomic Number<br>Z = Number of Protons<\/li>\n\n\n\n<li>Mass Number<br>A = Number of Protons + Number of Neutrons<\/li>\n\n\n\n<li>Number of Neutrons<br>Neutrons = Mass Number &minus; Atomic Number<\/li>\n\n\n\n<li>Maximum Electrons in Shell<br>2n&sup2;<\/li>\n\n\n\n<li>Average Atomic Mass<br>Average Mass = &Sigma;(Isotopic Mass &times; Abundance)\/100<\/li>\n<\/ol>\n\n\n\n<h1 class=\"wp-block-heading\">Questions &amp; Step-by-step Solutions with Explanation<\/h1>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h1 class=\"wp-block-heading has-luminous-vivid-orange-color has-text-color has-link-color wp-elements-2d29058ecf7012e9265a0ef97458be4f\">Pause and Ponder<\/h1>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Suppose you made up your own &lsquo;atom&rsquo;, as Thomson described, using clay for the positive charge and small beads for the electrons spread through it. What will happen if:<br>(i) the positive charge on the clay is lesser than the total negative charge of the beads?<br>(ii) by mistake, the clay itself carries a bit of negative charge? Would your model still represent a neutral atom?<\/li>\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-large\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-108-1024x683.png\" alt=\"image\" class=\"wp-image-3392\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-108-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-108-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-108-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-108.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">2. Could an orange or a lemon, which also contain seeds inside soft pulp, be a good comparison? In what ways does it match Thomson&rsquo;s idea and where does it fall short?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" width=\"1024\" height=\"819\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-109-1024x819.png\" alt=\"image\" class=\"wp-image-3393\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-109-1024x819.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-109-300x240.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-109-768x615.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-109.png 1402w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">3. Why did Thomson conclude that electrons are present in all atoms?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" width=\"932\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-110-932x1024.png\" alt=\"image\" class=\"wp-image-3394\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-110-932x1024.png 932w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-110-273x300.png 273w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-110-768x844.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-110.png 1197w\" sizes=\"(max-width: 932px) 100vw, 932px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">4. What do you think would happen if &alpha;-particles were replaced with negatively charged particles in Rutherford&rsquo;s gold foil experiment?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"949\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-111-949x1024.png\" alt=\"image\" class=\"wp-image-3395\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-111-949x1024.png 949w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-111-278x300.png 278w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-111-768x829.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-111.png 1207w\" sizes=\"(max-width: 949px) 100vw, 949px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">5. Rutherford found that a few &alpha;-particles bounced back sharply. How does this single surprising result completely rule out Thomson&rsquo;s &#699;plum pudding model&#700; of the atom?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"952\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-112-952x1024.png\" alt=\"image\" class=\"wp-image-3396\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-112-952x1024.png 952w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-112-279x300.png 279w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-112-768x826.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-112.png 1209w\" sizes=\"(max-width: 952px) 100vw, 952px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">6. If you could ask Rutherford one question about his work, what would it be?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"819\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-113-1024x819.png\" alt=\"image\" class=\"wp-image-3399\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-113-1024x819.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-113-300x240.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-113-768x615.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-113.png 1402w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<div class=\"internal-linking-related-contents\"><a href=\"https:\/\/mymockmate.com\/notes\/class-9-maths-exercise-1-1-solutions-coordinate-geometry-ncert-solutions\/\" class=\"template-2\"><span class=\"cta\">Related Topic to Read more<\/span><span class=\"postTitle\">NCERT Class 9 Maths Exercise 1.1 Solutions | Coordinate Geometry NCERT Solutions<\/span><\/a><\/div><p class=\"wp-block-paragraph\">7. Assertion (A): Rutherford concluded that most of the mass of an atom is concentrated in a small region at the centre called the nucleus.<br>Reason (R): According to Thomson&rsquo;s model, electrons are embedded in a uniformly distributed positive charge sphere.<br>Choose the correct option:<br>(i) Both A and R are true, and R is the correct explanation of A.<br>(ii) Both A and R are true, but R is not the correct explanation of A.<br>(iii) A is true, but R is false.<br>(iv) A is false, but R is true<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-114-1024x683.png\" alt=\"image\" class=\"wp-image-3400\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-114-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-114-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-114-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-114.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">8. Imagine you are a scientist who has discovered a new element. Name this element after yourself and justify that the symbol you have chosen follows the IUPAC rules.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"936\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-115-936x1024.png\" alt=\"image\" class=\"wp-image-3401\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-115-936x1024.png 936w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-115-274x300.png 274w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-115-768x840.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-115.png 1199w\" sizes=\"(max-width: 936px) 100vw, 936px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">9. What problems could arise if every scientist used different symbols for the same element?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"962\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-116-962x1024.png\" alt=\"image\" class=\"wp-image-3402\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-116-962x1024.png 962w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-116-282x300.png 282w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-116-768x817.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-116.png 1216w\" sizes=\"(max-width: 962px) 100vw, 962px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">10. An atom with an atomic number of 26 has 56 nucleons. Find out its number of electrons, protons and neutrons.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"859\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-117-859x1024.png\" alt=\"image\" class=\"wp-image-3403\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-117-859x1024.png 859w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-117-252x300.png 252w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-117-768x915.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-117.png 1149w\" sizes=\"(max-width: 859px) 100vw, 859px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">11. The nucleus of an atom contains 20 protons. If its mass number is 41, find the number of neutrons in it.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"819\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-118-1024x819.png\" alt=\"image\" class=\"wp-image-3404\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-118-1024x819.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-118-300x240.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-118-768x615.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-118.png 1402w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">12. An atom has 18 neutrons and an atomic number of 17. What is its mass number?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"819\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-121-1024x819.png\" alt=\"image\" class=\"wp-image-3407\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-121-1024x819.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-121-300x240.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-121-768x615.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-121.png 1402w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<div class=\"internal-linking-related-contents\"><a href=\"https:\/\/mymockmate.com\/notes\/class-9-maths-exercise-1-2-solutions-coordinate-geometry-ncert-solutions\/\" class=\"template-2\"><span class=\"cta\">Related Topic to Read more<\/span><span class=\"postTitle\">NCERT Class 9 Maths Exercise 1.2 Solutions | Coordinate Geometry NCERT Solutions<\/span><\/a><\/div><p class=\"wp-block-paragraph\">13. An atom <sup>23<\/sup>A has 11 electrons. Find the number of neutrons in it.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"909\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-120-909x1024.png\" alt=\"image\" class=\"wp-image-3406\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-120-909x1024.png 909w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-120-266x300.png 266w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-120-768x866.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-120.png 1181w\" sizes=\"(max-width: 909px) 100vw, 909px\"><\/figure>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"779\" height=\"155\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-119.png\" alt=\"image\" class=\"wp-image-3405\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-119.png 779w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-119-300x60.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-119-768x153.png 768w\" sizes=\"(max-width: 779px) 100vw, 779px\"><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"819\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-122-1024x819.png\" alt=\"image\" class=\"wp-image-3408\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-122-1024x819.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-122-300x240.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-122-768x615.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-122.png 1402w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">15. Write the electronic configuration of the elements having atomic numbers 12, 16 and 18.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-123-1024x683.png\" alt=\"image\" class=\"wp-image-3409\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-123-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-123-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-123-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-123.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">16. Solve this riddle: I am an atom with a mass number of 23 and 11 protons. I am a soft metal and react vigorously with water. Who am I and how many neutrons do I have? You can also create one such riddle.<\/p><div class=\"mymoc-middle mymoc-entity-placement\" id=\"mymoc-497301181\"><div id=\"mymoc-924249005\"><a href=\"https:\/\/amzn.to\/4uMTpup\" aria-label=\"books\"><img src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/books.png\" alt=\"\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/books.png 1301w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/books-300x56.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/books-1024x190.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/books-768x143.png 768w\" sizes=\"(max-width: 1301px) 100vw, 1301px\" width=\"1301\" height=\"242\"><\/a><\/div><\/div>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"966\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-124-966x1024.png\" alt=\"image\" class=\"wp-image-3410\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-124-966x1024.png 966w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-124-283x300.png 283w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-124-768x814.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-124.png 1218w\" sizes=\"(max-width: 966px) 100vw, 966px\"><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">17. Two different atoms have 11 protons each, but one has 12 neutrons, and the other has 13 neutrons. How do their<br>atomic numbers and mass numbers compare? Are they the same element or different elements?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"928\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-127-928x1024.png\" alt=\"image\" class=\"wp-image-3413\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-127-928x1024.png 928w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-127-272x300.png 272w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-127-768x847.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-127.png 1194w\" sizes=\"(max-width: 928px) 100vw, 928px\"><\/figure>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"593\" height=\"79\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-125.png\" alt=\"image\" class=\"wp-image-3411\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-125.png 593w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-125-300x40.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-125-590x79.png 590w\" sizes=\"(max-width: 593px) 100vw, 593px\"><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-128-1024x683.png\" alt=\"image\" class=\"wp-image-3414\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-128-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-128-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-128-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-128.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<h1 class=\"wp-block-heading has-text-align-center has-vivid-red-color has-text-color has-link-color wp-elements-f7bf5b9316920b179dbe01b15d7fbf2b\">Revise, Reflect, Refine<\/h1>\n\n\n\n<h2 class=\"wp-block-heading\">Q1. Choose the correct options and explain the reason for the correct and incorrect options in the context of Ernest Rutherford&rsquo;s gold foil experiment:<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">(i) The experiment clearly showed the existence of neutrons in the nucleus.<br>(ii) The results disproved the plum pudding model and led to the idea of a nucleus at the centre of the atom.<br>(iii) The large deflection of a few alpha particles indicated that most of the mass of the atom and positive charge are packed into a tiny centre.<br>(iv) The way alpha particles were deflected showed that electrons move around the nucleus.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"866\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-129-866x1024.png\" alt=\"image\" class=\"wp-image-3417\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-129-866x1024.png 866w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-129-254x300.png 254w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-129-768x909.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-129.png 1153w\" sizes=\"(max-width: 866px) 100vw, 866px\"><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Q2. Which of the following statements are correct or incorrect according to the Bohr&rsquo;s atomic model? Give a reason for each statement.<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">(i) Electrons lose energy while moving in fixed orbits and slowly fall into the nucleus.<br>(ii) Electrons can exist anywhere around the nucleus with no fixed energy.<br>(iii) Electrons revolve around the nucleus in orbits of fixed energy without losing energy.<br>(iv) Electrons can be found between energy levels as they move around the nucleus.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"908\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-130-908x1024.png\" alt=\"image\" class=\"wp-image-3418\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-130-908x1024.png 908w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-130-266x300.png 266w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-130-768x866.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-130.png 1181w\" sizes=\"(max-width: 908px) 100vw, 908px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"786\" height=\"320\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-131.png\" alt=\"image\" class=\"wp-image-3419\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-131.png 786w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-131-300x122.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-131-768x313.png 768w\" sizes=\"(max-width: 786px) 100vw, 786px\"><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-132-1024x683.png\" alt=\"image\" class=\"wp-image-3420\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-132-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-132-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-132-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-132.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q4. What conclusion did Rutherford draw about the position and characteristics of the atom&rsquo;s positively charged part based on the few alpha particles that bounced back or were deflected at large angles in<br>the gold foil experiment?<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Solution:<\/h3>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"909\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-133-909x1024.png\" alt=\"image\" class=\"wp-image-3421\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-133-909x1024.png 909w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-133-266x300.png 266w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-133-768x866.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-133.png 1181w\" sizes=\"(max-width: 909px) 100vw, 909px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q5. Explain and arrange the following statements in the correct chronological order to show how atomic models have evolved over time.<\/h2>\n\n\n\n<div class=\"internal-linking-related-contents\"><a href=\"https:\/\/mymockmate.com\/notes\/class-9-maths-end-of-chapter-exercise-solutions-coordinate-geometry-ncert-solutions\/\" class=\"template-2\"><span class=\"cta\">Related Topic to Read more<\/span><span class=\"postTitle\">NCERT Class 9 Maths End of Chapter Exercise Solutions | Coordinate Geometry<\/span><\/a><\/div><p class=\"wp-block-paragraph\">(i) Bohr&rsquo;s model proposed that electrons move in fixed orbits around the nucleus, each with a definite energy.<br>(ii) Thomson&rsquo;s model depicted the atom as a &#699;plum pudding&#700; with electrons embedded in a sphere of positive charge.<br>(iii) Rutherford&rsquo;s model proposed that atoms have a dense central nucleus.<br>(iv) Dalton&rsquo;s model described atoms as indivisible particles.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"884\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-134-884x1024.png\" alt=\"image\" class=\"wp-image-3422\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-134-884x1024.png 884w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-134-259x300.png 259w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-134-768x890.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-134.png 1165w\" sizes=\"(max-width: 884px) 100vw, 884px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q6. Electrons move around the nucleus in orbits. Why do they not fly away<br>from the atom? Explain what keeps them attracted to the nucleus.<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Solution:<\/h3>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"887\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-135-887x1024.png\" alt=\"image\" class=\"wp-image-3423\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-135-887x1024.png 887w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-135-260x300.png 260w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-135-768x886.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-135.png 1167w\" sizes=\"(max-width: 887px) 100vw, 887px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q7. Assertion&thinsp;(A):&thinsp;&thinsp;The discovery of subatomic particles helped in<br>understanding the atomic structure.<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Reason (R): The number of electrons is equal to the number of protons in an atom.<br>Choose the correct option:<br>(i) Both A and R are true, and R is the correct explanation of A.<br>(ii) Both A and R are true, but R is not the correct explanation of A.<br>(iii) A is true, but R is false.<br>(iv) A is false, but R is true.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-136-1024x683.png\" alt=\"image\" class=\"wp-image-3424\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-136-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-136-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-136-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-136.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q8. Magnesium is essential for many biological processes, including<br>muscle contraction. For an atom of magnesium with a mass number<br>of 24 and atomic number 12, determine the number of <\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">(i) protons,<br>(ii) neutrons, (iii) electrons, and also illustrate the arrangement of electrons in a magnesium atom.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"859\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-138-859x1024.png\" alt=\"image\" class=\"wp-image-3426\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-138-859x1024.png 859w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-138-252x300.png 252w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-138-768x915.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-138.png 1149w\" sizes=\"(max-width: 859px) 100vw, 859px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h1 class=\"wp-block-heading\"><\/h1>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"748\" height=\"485\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-137.png\" alt=\"image\" class=\"wp-image-3425\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-137.png 748w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-137-300x195.png 300w\" sizes=\"(max-width: 748px) 100vw, 748px\"><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-139-1024x683.png\" alt=\"image\" class=\"wp-image-3427\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-139-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-139-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-139-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-139.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q10. Both Rutherford&rsquo;s and Bohr&rsquo;s models have electrons orbiting the<br>nucleus. Why did Rutherford&rsquo;s model fail to explain atomic stability,<br>while Bohr&rsquo;s model succeeded?<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><\/h3>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-140-1024x683.png\" alt=\"image\" class=\"wp-image-3428\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-140-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-140-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-140-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-140.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q11. An atom <sup>70&thinsp;&thinsp;<\/sup>X has 31 electrons. How many neutrons are there in its nucleus?<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-142-1024x683.png\" alt=\"image\" class=\"wp-image-3432\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-142-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-142-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-142-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-142.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q12. An atom has 79 protons and a mass number of 197. Calculate <\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">(i) the number of neutrons, and <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">(ii) the number of electrons.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><\/h3>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"819\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-143-1024x819.png\" alt=\"image\" class=\"wp-image-3433\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-143-1024x819.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-143-300x240.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-143-768x615.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-143.png 1402w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"785\" height=\"308\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-145.png\" alt=\"image\" class=\"wp-image-3435\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-145.png 785w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-145-300x118.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-145-768x301.png 768w\" sizes=\"(max-width: 785px) 100vw, 785px\"><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-148-1024x683.png\" alt=\"image\" class=\"wp-image-3440\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-148-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-148-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-148-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-148.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q14. Aman was discussing the structure of atom with his classmates.<br>During the discussion, he learnt that an element X has a mass number<br>of 35 and contains 18 neutrons. Based on this information, answer the<br>following questions:<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">(i) How many electrons and protons does element X have?<br>(ii) What is its atomic number?<br>(iii) Identify the element X.<br>(iv) Write its electronic configuration.<br>(v) How many valence electrons does it have?<br>(vi) What will be the mass number if two neutrons are added to its nucleus?<br>(vii) What will be the relation of X with the new atom?<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"930\" height=\"1024\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-146-930x1024.png\" alt=\"image\" class=\"wp-image-3436\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-146-930x1024.png 930w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-146-272x300.png 272w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-146-768x846.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-146.png 1195w\" sizes=\"(max-width: 930px) 100vw, 930px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h2 class=\"wp-block-heading\">Q15. In an atom, there are 12 protons and 12 neutrons in the nucleus.<br>Now, imagine that all the electrons are replaced with some hypothetical<br>particles that have the same charge as electrons but are 500 times<br>heavier. What effect will this replacement have on the atom&rsquo;s:<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">(i) Atomic number<br>(ii) Atomic mass<br>(iii) Mass number<br>(iv) Overall charge<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-147-1024x683.png\" alt=\"image\" class=\"wp-image-3437\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-147-1024x683.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-147-300x200.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-147-768x512.png 768w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/image-147.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h1 class=\"wp-block-heading\">Common Mistakes<\/h1>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Confusing atomic number with mass number<\/li>\n\n\n\n<li>Forgetting neutrons calculation<\/li>\n\n\n\n<li>Writing incorrect shell capacities<\/li>\n\n\n\n<li>Mixing isotopes and isobars<\/li>\n\n\n\n<li>Incorrect electronic configuration<\/li>\n<\/ul>\n\n\n\n<h1 class=\"wp-block-heading\">Exam Tips<\/h1>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Learn all atomic models in sequence.<\/li>\n\n\n\n<li>Practice electron distribution regularly.<\/li>\n\n\n\n<li>Remember formulas for atomic number and mass number.<\/li>\n\n\n\n<li>Revise isotopes and isobars carefully.<\/li>\n\n\n\n<li>Draw neat atomic diagrams in exams.<\/li>\n<\/ul>\n\n\n\n<h1 class=\"wp-block-heading\">Practice MCQs<\/h1>\n\n\n\n<h3 class=\"wp-block-heading\">1. Who discovered the nucleus?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A. Dalton<br>B. Rutherford<br>C. Bohr<br>D. Chadwick<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Answer:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">B. Rutherford<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h3 class=\"wp-block-heading\">2. Maximum electrons in K-shell:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A. 8<br>B. 18<br>C. 2<br>D. 32<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Answer:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">C. 2<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h3 class=\"wp-block-heading\">3. Atomic number equals:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A. Neutrons<br>B. Electrons + Neutrons<br>C. Protons<br>D. Mass number<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Answer:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">C. Protons<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h3 class=\"wp-block-heading\">4. Isotopes have:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A. Same mass number<br>B. Same atomic number<br>C. Different electrons only<br>D. Same neutrons<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Answer:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">B. Same atomic number<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\">\n\n\n\n<h3 class=\"wp-block-heading\">5. Scientist who discovered neutron:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A. Bohr<br>B. Rutherford<br>C. Chadwick<br>D. Thomson<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Answer:<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">C. Chadwick<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">FAQ Section<\/h1>\n\n\n\n<h3 class=\"wp-block-heading\">Q1. What is atomic number?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Atomic number is the number of protons in an atom.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Q2. What is mass number?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Mass number is total number of protons and neutrons.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Q3. What are isotopes?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Atoms with same atomic number but different mass numbers.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Q4. What are isobars?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Atoms with same mass number but different atomic numbers.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Q5. Why are noble gases stable?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Because they have complete outermost electron shells.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Prepare smarter with chapter-wise notes, solved questions, MCQs, quizzes, and mock tests only on <a href=\"http:\/\/www.mymockmate.com\/\">www.mymockmate.com<\/a> and boost your exam performance today!<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n<div class=\"pdfprnt-buttons pdfprnt-buttons-post pdfprnt-top-bottom-right\"><a href=\"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/posts\/2515?print=print\" class=\"pdfprnt-button pdfprnt-button-print\" target=\"_blank\"><img decoding=\"async\" src=\"https:\/\/mymockmate.com\/notes\/wp-content\/plugins\/pdf-print\/images\/print.png\" alt=\"image_print\" title=\"Print Content\"><span class=\"pdfprnt-button-title pdfprnt-button-print-title\">Print<\/span><\/a> <span class=\"pdfprnt-count-generation\">16<\/span><\/div><div class=\"mymoc-bottom mymoc-entity-placement\" id=\"mymoc-637314166\"><div id=\"mymoc-1288689042\"><a href=\"https:\/\/amzn.to\/4ehJfM4\" aria-label=\"students acessories\"><img src=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/students-acessories.png\" alt=\"\" srcset=\"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/students-acessories.png 1301w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/students-acessories-300x85.png 300w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/students-acessories-1024x290.png 1024w, https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/06\/students-acessories-768x218.png 768w\" sizes=\"(max-width: 1301px) 100vw, 1301px\" width=\"1080\" height=\"100\"><\/a><\/div><\/div>","protected":false},"excerpt":{"rendered":"<p> 16 Short Intro This chapter explains the fascinating journey of discovering the structure of the atom. Students learn about atomic models proposed by Dalton,&#8230;<\/p>\n","protected":false},"author":3,"featured_media":2518,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"postBodyCss":"","postBodyMargin":[],"postBodyPadding":[],"postBodyBackground":{"backgroundType":"classic","gradient":""},"footnotes":""},"categories":[4,12],"tags":[1365,1366,1363,1359,1368,1369,1367,1364,1370],"class_list":["post-2515","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-class-9","category-science","tag-atom-structure","tag-atomic-number","tag-bohr-model","tag-class-9-science","tag-isobars","tag-isotopes","tag-mass-number","tag-rutherford-model","tag-valency"],"featured_image_src":"https:\/\/mymockmate.com\/notes\/wp-content\/uploads\/2026\/05\/NCERT-Class-9-Science-Journey-Inside-the-Atom-Question-Answers.png","author_info":{"display_name":"Team Mymockmate (L)","author_link":"https:\/\/mymockmate.com\/notes\/author\/luckp\/"},"_links":{"self":[{"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/posts\/2515","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/comments?post=2515"}],"version-history":[{"count":8,"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/posts\/2515\/revisions"}],"predecessor-version":[{"id":4248,"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/posts\/2515\/revisions\/4248"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/media\/2518"}],"wp:attachment":[{"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/media?parent=2515"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/categories?post=2515"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mymockmate.com\/notes\/wp-json\/wp\/v2\/tags?post=2515"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}