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CBSE Class 9  >  Class 9 Test  >  Online MCQ Tests  >  Test: Atomic Number, Mass Number and isotopes - Class 9 MCQ

Atomic Number, Mass Number and isotopes - Free MCQ Practice Test with solutions,


MCQ Practice Test & Solutions: Test: Atomic Number, Mass Number and isotopes (20 Questions)

You can prepare effectively for Class 9 Online MCQ Tests for Class 9 with this dedicated MCQ Practice Test (available with solutions) on the important topic of "Test: Atomic Number, Mass Number and isotopes". These 20 questions have been designed by the experts with the latest curriculum of Class 9 2026, to help you master the concept.

Test Highlights:

  • - Format: Multiple Choice Questions (MCQ)
  • - Duration: 20 minutes
  • - Number of Questions: 20

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Test: Atomic Number, Mass Number and isotopes - Question 1
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Which of the following element is used in the treatment of cancer?

Detailed Solution: Question 1

Elements Used in Radiation Therapy. Radiation therapy is an important cancer treatment along with chemotherapy and surgery. The most famous type is probably gamma ray irradiation by radioactive cobalt-60.

Test: Atomic Number, Mass Number and isotopes - Question 2
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21H and 31H are _______ .​

Detailed Solution: Question 2

Atoms of the same element having the same atomic numbers but different mass numbers are termed as isotopes.

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Test: Atomic Number, Mass Number and isotopes - Question 3
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Which one of the following statements is correct about isotopes?

Detailed Solution: Question 3

Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.

Test: Atomic Number, Mass Number and isotopes - Question 4
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The two isotopes of chlorine are 3517Cl and 3717Cl in the ratio of 3:1. What is the average atomic mass of the chlorine atom?​

Detailed Solution: Question 4

Average atomic mass of chlorine is given by:

(35 x 3) + (37 x 1)/4 = 35.50 u

Test: Atomic Number, Mass Number and isotopes - Question 5
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Which one of the following statements is incorrect?

Test: Atomic Number, Mass Number and isotopes - Question 6
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Argon has atomic number of 18 and mass number of 40. Calcium has atomic 20 and mass number 40. Calcium and argon are examples of _______.

Detailed Solution: Question 6

Atoms of different elements with different atomic numbers and the same mass number are known as isobars. 

Test: Atomic Number, Mass Number and isotopes - Question 7
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The isotopic composition of a certain element X is 80% 24X, 10% 25X and 10% 26X. The relative-atomic mass of X is _______.​

Test: Atomic Number, Mass Number and isotopes - Question 8
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Atomic number is equal to:

Detailed Solution: Question 8

Its equal to no.of protons but mass number =no.of protons +no.of neutrons

Test: Atomic Number, Mass Number and isotopes - Question 9
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Why do isotopes have different physical properties?

Detailed Solution: Question 9

They have similar chemical properties because isotopes of an element have the same number of electrons as an atom of that element. The electron arrangement is the same owing to same chemical properties. However they have different numbers of neutrons, which affects the mass number. Mass number determines the physical properties such as boiling/melting/density etc

Test: Atomic Number, Mass Number and isotopes - Question 10
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An element B has 5 protons and 6 neutrons. What will be the symbol of the element B?​

Detailed Solution: Question 10

Atomic number of B = Number of Protons = Number of electron in element
= 5
Mass number = Number of protons + Number of neutrons = 5 + 6 = 11
So, symbol of B : 115B

Test: Atomic Number, Mass Number and isotopes - Question 11
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The atomic number of an element having mass number 23 and number of neutron 12 is ________.

Detailed Solution: Question 11

A neutral atom will have the same number of electrons is does protons. Since it has an atomic number of 11 it must have 11 protons. Since it has an atomic mass of 23 it must have 12 neutrons.

Test: Atomic Number, Mass Number and isotopes - Question 12
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Which form of iodine is used for the treatment of goiter?

Test: Atomic Number, Mass Number and isotopes - Question 13
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The total number of neutrons in 1224Mg2+is:​

Detailed Solution: Question 13

Mass of Mg = no.of protons + no.of neutrons
no.of protons = 12 [ atomic no. = no.of protons = 12]
mass of Mg = 24 
so, no.of neutrons = 12

Test: Atomic Number, Mass Number and isotopes - Question 14
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Neon occurs as two isotopes of mass numbers 20 and 22. Its relative atomic mass is 20.2. What is the percentage of 20Ne in naturally occurring neon?

Detailed Solution: Question 14

Let the relative abundance% of Ne -20 = x1
So, relative abundance% of Ne -22 =  x2

Now, we know that atomic mass = sum of relative abundance in atomic mass of each isotope / 100% 

20.2 = 20 x1 + 22 x2 / x1 +x2 
20.2 x1 + 20.2x2 = 20x1 + 22x2
0.2x1 =  1.8 x2 

x1 / x2  = 1.8/ 0.2 = 9/1   ( relative abundance) 

x1%  =  9/10 * 100  = 90%  lighter isotopes
x2%  =  1/ 10* 100  = 10%   heavier isotope 

Test: Atomic Number, Mass Number and isotopes - Question 15
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Which of the following elements has 17 electrons and 17 protons?

Detailed Solution: Question 15

The atomic number is the number of electrons present in an atom. We know that an atom has the same number of electrons & Protons. Therefore Chlorine is the element that has 17 protons. Hence the element is Chlorine.

Test: Atomic Number, Mass Number and isotopes - Question 16
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Find the symbol of an element X, if its mass number is A and atomic number is Z respectively.

Test: Atomic Number, Mass Number and isotopes - Question 17
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The atomic number and the mass number of an element A are 14 and 28 respectively. The number of neutrons are:

Detailed Solution: Question 17

Given, Z = 14  , A = 28 ;
 We know that Z = p=14
And, A = p + n ⇒ 28 = 14+n 
  n = 28 -14 
  n =  14 
Hence, no. Of neutrons are 14.

Test: Atomic Number, Mass Number and isotopes - Question 18
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Which of the following statement is correct for isotopes?

Test: Atomic Number, Mass Number and isotopes - Question 19
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An neutral element A has 3 electrons, the atomic number of an element is _______.

Test: Atomic Number, Mass Number and isotopes - Question 20
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An atom is represented by symbol 2314M. What does the number 23 represent?​

Detailed Solution: Question 20

Nucleons reside inside the nucleus and are denoted by the mass number is denoted as “A.” All atoms of a particular chemical element will have the same atomic number, number of protons present in the nucleus of an atom, but different mass numbers.

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About this Class 9 Practice Test

This test contains 20 MCQs on Atomic Number, Mass Number and isotopes with detailed solutions for each question. It is part of the Online MCQ Tests for Class 9 course on EduRev, designed to align with the current Class 9 syllabus. Each solution explains not just the correct answer but also gives you an understanding of the topic — not just to attempt the question but also help you prepare for the exam with practice.

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