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# Test: Atomic Number, Mass Number and isotopes

## 20 Questions MCQ Test Science Class 9 | Test: Atomic Number, Mass Number and isotopes

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This mock test of Test: Atomic Number, Mass Number and isotopes for Class 9 helps you for every Class 9 entrance exam. This contains 20 Multiple Choice Questions for Class 9 Test: Atomic Number, Mass Number and isotopes (mcq) to study with solutions a complete question bank. The solved questions answers in this Test: Atomic Number, Mass Number and isotopes quiz give you a good mix of easy questions and tough questions. Class 9 students definitely take this Test: Atomic Number, Mass Number and isotopes exercise for a better result in the exam. You can find other Test: Atomic Number, Mass Number and isotopes extra questions, long questions & short questions for Class 9 on EduRev as well by searching above.
QUESTION: 1

### Which of the following element is used in the treatment of cancer?

Solution: 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.
QUESTION: 2

### 21H and 31H are _______ .​

Solution:

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

QUESTION: 3

### Which one of the following statements is correct about isotopes?

Solution: 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.
QUESTION: 4

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?​

Solution:

Average atomic mass of chlorine is given by:

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

QUESTION: 5

Which one of the following statements is incorrect?

Solution:
QUESTION: 6

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 _______.

Solution:

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

QUESTION: 7

The isotopic composition of a certain element X is 80% 24X, 10% 25X and 10% 26X. The relative-atomic mass of X is _______.​

Solution:
QUESTION: 8

Atomic number is equal to:

Solution: Its equal to no.of protons but mass number =no.of protons +no.of neutrons
QUESTION: 9

Why do isotopes have different physical properties?

Solution:

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

QUESTION: 10

An element B has 5 protons and 6 neutrons. What will be the symbol of the element B?​

Solution:

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

QUESTION: 11

The atomic number of an element having mass number 23 and number of neutron 12 is ________.

Solution: 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.
QUESTION: 12

Which form of iodine is used for the treatment of goiter?

Solution:
QUESTION: 13

The total number of neutrons in 1224Mg2+is:​

Solution: 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

QUESTION: 14

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?

Solution:

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

QUESTION: 15

Which of the following elements has 17 electrons and 17 protons?

Solution:

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.

QUESTION: 16

Find the symbol of an element X, if its mass number is A and atomic number is Z respectively.

Solution:
QUESTION: 17

The atomic number and the mass number of an element A are 14 and 28 respectively. The number of neutrons are:

Solution:

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.

QUESTION: 18

Which of the following statement is correct for isotopes?

Solution:
QUESTION: 19

An neutral element A has 3 electrons, the atomic number of an element is _______.

Solution:
QUESTION: 20

An atom is represented by symbol 2314M. What does the number 23 represent?​

Solution: 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.