Do you need help learning for your Class 12 Physics exam? Students may want to download NCERT MCQ Questions for Class 12 Physics Chapter 13 Nuclei with Answers Pdf free download. These Nuclei Class 12 MCQs Questions with Answers can help understand the concepts score better in your Class 12 Physics Exam, so make sure you practice these! Check out chapter-wise MCQ Questions for Class 12 Physics with Answers.

## Nuclei Class 12 MCQs Questions with Answers

Solve these Nuclei Multiple Choice Questions of Class 12 Physics Chapter 13 MCQ, so as not to miss out on any concept from being clear about what they mean!

I. Choose the correct answer

Question 1.

When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom

(a) do not change for any type of radioactivity.

(b) change for α and ß radioactivity but not for γ-radioactivity.

(c) change for α-radioactivity but not for others.

(d) change for ß-radioactivity but not for others.

## Answer

Answer: (b) change for α and ß radioactivity but not for γ-radioactivity.

Question 2.

A radioactive isotope has a half-life of T years. The time it takes its activity to reduce to 3.125% is

(a) 5 T

(b) 6.654 T

(c) 5.645 T

(d) 6.654 T

## Answer

Answer: (a) 5 T

Question 3.

For a radioactive material, half-life is 10 minutes. If initially there are 600 number of nuclei, the time taken (in minutes) for the disintegration of 450 nuclei is:

(a) 20

(b) 10

(c) 30

(d) 15

## Answer

Answer: (a) 20

Question 4.

A nuclear explosive is designed to deliver 1 MW power in the form of heat energy. If the explosion is designed with nuclear fuel consisting of U^{235} to run a reactor at this power level for one year, then the amount of fuel needed is (given energy per fission is 200 MeV)

(a) 1 kg

(b) 0.01 kg

(c) 3.84 kg

(d) 0.384 kg

## Answer

Answer: (d) 0.384 kg

Question 5.

When the radioactive isotope _{88}Ra^{226} decays in a series by emission of three alpha (α) and a beta (ß) particle, the isotope X which remains undecayed is

(a) _{83}X^{214}

(b) _{84}X^{218}

(c) _{84}X^{220}

(d) _{87}X^{223}

## Answer

Answer: (a) _{83}X^{214}

Question 6.

Fusion reaction takes place, at high temperature because:

(a) nuclei break up at high temperature

(b) atoms get ionised at high temperature

(c) kinetic energy is high enough to overcome the coulomb repulsion between nuclei

(d) molecules break up at high temperature

## Answer

Answer: (c) kinetic energy is high enough to overcome the coulomb repulsion between nuclei

Question 7.

Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes, respectively. Initially, the samples have equal number of nuclei. After 80 minutes, the ratio of decayed numbers of A and B nuclei will be:

(a) 1 : 16

(b) 4 : 1

(c) 1 : 4

(d) 5 : 4

## Answer

Answer: (d) 5 : 4

Question 8.

Radioactive material ‘A’ has decay constant ‘8 λ’ and material ‘B’ has decay constant ‘λ’. Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material ‘B’ to that ‘A’ will be 1/e?

(a) \(\frac { 1 }{7λ}\)

(b) \(\frac { 1 }{8λ}\)

(c) \(\frac { 1 }{9λ}\)

(d) \(\frac { 1 }{λ}\)

## Answer

Answer: (a) \(\frac { 1 }{7λ}\)

Question 9.

A radioactive nucleus A with a half-life T decays into a nucleus B. At t = 0, there is no nucleus B. At some time, t the ratio of the number of B to that of A is 0.3. Then, t is given by:

(a) t = T log(1.3)

(b) t = \(\frac { T }{log(1.3)}\)

(c) t = \(\frac { T log(2) }{2log(1.3)}\)

(d) t = \(\frac { T log(1.3) }{log(2)}\)

## Answer

Answer: (d) t = \(\frac { T log(1.3) }{log(2)}\)

II. Fill in the blanks

Question 1.

Isotopes of an element are the atoms of an element which have ……………….. but different atomic weights.

## Answer

Answer: Same atomic number

Question 2.

Isobars are the atoms of different elements which have same ……………….. but different atomic number.

## Answer

Answer: Atomic weights

Question 3.

Isotones are the nuclides which contain ………………..

## Answer

Answer: Same no. of neutrons

Question 4.

One atomic mass unit is defined as ……………….. of mass of an atom of ^{6}C_{12}

## Answer

Answer: (1 /12th)

Question 5.

Nuclear forces are the ……………….. force which hold together the nucleons in the tiny nucleus.

## Answer

Answer: strongest

Question 6.

Nuclear forces are ……………….. Independent.

## Answer

Answer: Charge

Question 7.

Nuclear forces do not obey ……………….. law.

## Answer

Answer: Inverse square

Question 8.

The rest mass of a nucleus Is ……………….. than the sum of the rest masses of Its constituent nucleons.

## Answer

Answer: Less [Mass defect]

Question 9.

The total energy required to liberate all the nucleons from the nucleus, i.e. to disintegrate the nucleus into its constituent particles, is called ………………..

## Answer

Answer: Nuclear binding energy

Question 10.

The divergence of the nuclear mass from the nearest whole number (mass number) per nucleon is called ………………..

## Answer

Answer: Packing fraction

Question 11.

Natural ……………….. is defined as the spontaneous disintegration of a nucleus with the emission of certain particles and radiation.

## Answer

Answer: Radioactivity

Question 12.

During alpha decay atomic number of the daughter nucleus decreases by ……………….. and mass number decreases by ………………..

## Answer

Answer: 2, 4

Question 13.

In negative beta decay there is no change in ………………..

## Answer

Answer: Mass number

Question 14.

The energy distribution of beta decay is ………………..

## Answer

Answer: Continuous

Question 15.

The number of nuclei disintegrating per second is ……………….. to the number of nuclei present at the time of disintegration.

## Answer

Answer: Proportional

Question 16.

A ……………….. is defined as the reciprocal of that time duration for which the number of nuclei of the radioactive sample decays to 1/e.

## Answer

Answer: Decay constant

Question 17.

The ……………….. is the time required for the number of radioactive nuclei to decrease to one-half the original number.

## Answer

Answer: Half-life

Question 18.

A radioactive isotope of silver has half-life of 20 minutes. Tb fraction of the original activity that remains after one hour is ………………..

## Answer

Answer: 1/8

Question 19.

The rate of disintegration in a radioactive substance is known as its ………………..

## Answer

Answer: Activity.

Question 20.

The activity of a sample is said to be one ……………….. if it undergoes one decay per second.

## Answer

Answer: Becquerel

Question 21.

Heavy water is a ……………….. which slows down fast moving neutrons to thermal velocities so that they can cause fission of ^{235}U_{92 }nuclei.

## Answer

Answer: Moderator

Question 22.

Two nuclei have mass numbers in the ratio 27 : 125. Then the ratio of their radii is ………………..

## Answer

Answer: 3 : 5

Question 23.

Complete the equation

is …………………

## Answer

Answer: \(_{ n-2 }^{m-4}\)Y

Question 24.

The process responsible for energy production in the Sun is ………………..

## Answer

Answer: Nuclear fusion

This NCERT MCQ Questions for Class 12 Physics Chapter 13 Nuclei with Answers Pdf free download has been put together to help students understand the CBSE Class 12 Physics Nuclei MCQs Multiple Choice Questions with Answers. Hope you found this helpful!