# MCQs for Physics Class 12 with Answers Chapter 13 Nuclei

Students of class 12 Physics should refer to MCQ Questions Class 12 Physics Nuclei with answers provided here which is an important chapter in Class 12 Physics NCERT textbook. These MCQ for Class 12 Physics with Answers have been prepared based on the latest CBSE and NCERT syllabus and examination guidelines for Class 12 Physics. The following MCQs can help you to practice and get better marks in the upcoming class 12 Physics examination

## Chapter 13 Nuclei MCQ with Answers Class 12 Physics

MCQ Questions Class 12 Physics Nuclei provided below have been prepared by expert teachers of grade 12. These objective questions with solutions are expected to come in the upcoming Standard 12 examinations. Learn the below provided MCQ questions to get better marks in examinations.

Question. During a mean life of a radioactive element the fraction that disintegrates is:

C

Question. The gravitational force between a H-atom and another particle of mass m will be given by Newton’s law:

B

Question. 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.
(c) change for a-radioactivity but not for others.
(d) change for β-radioactivity but not for others.

B

Question. A nuclear reaction is given below. The masses in amu of reactant and product nuclei are given in brackets:

The value of energy Q is
(a) 1.234 MeV
(b) 0.91 MeV
(c) 0.465 MeV
(d) 1.862 MeV

D

Question. When boron (105B ) is bombarded by neutron, alpha-particles is emitted. The resulting nucleushas the mass number
(a) 11
(b) 7
(c) 6
(d) 15

B

Question. The binding energies per nucleon of deuteron (1H2) and helium (2He4) nuclei are 1.1 MeV and 7 MeV respectively. If two deuterons fuse together to form a helium nucleus, then energy produced is:
(a) 5.9 MeV
(b) 23.6 MeV
(c) 26.9 MeV
(d) 32.4 MeV

B

Question. Mx and My denote the atomic masses of the parent and the daughter nuclei respectively in a radioactive decay. The Q-value for a β decay is Q1 and that for a β+ decay is Q2. If me denotes the mass of an electron, then which of the following statements is correct?
(a) Q1 = (Mx – My) c2 = and Q2 = (Mx – My – 2me)c2
(b) Q1 = (Mx – My)c2 and Q2 = (Mx – My )c2
(c) Q1 = (Mx – My – 2 me) c2 and Q2 = (Mx – My +2 me)c2
(d) Q1 = (Mx – My + 2 me) c2 and Q2 = (Mx – My +2 me)c2

A

Question. How much energy will approximately be released if all the atoms of 1 kg of deuterium could undergo fusion? [Assume energy released per deuterium nucleus is 2 MeV]
(a) 2 × 107 kWh
(b) 9 × 1013 J
(c) 6 × 1027 calorie
(d) 9 × 1013 MeV

B

Question. The half life of 215 At is 100 μs. The time taken for the activity of the sample of 215 At to decay to 1/16
th of its initial value is

(a) 400 μs
(b) 300 μs
(c) 40 μs
(d) 6.3 μs

A

Question. Samples of two radioactive nuclides A and B are taken. λA and λB are the disintegration constants of A and B respectively. In which of the following cases, the two samples can simultaneously have the same decay rate at any time?
(a) Initial rate of decay of A is twice the initial rate of decay of B and λA = λB.
(b) Initial rate of decay of A is twice the initial rate of decay of B and λA > λB.
(c) Initial rate of decay of B is twice the initial rate of decay of A and λA > λB.
(d) Initial rate of decay of B is same as the rate of decay of A at t = 2h and λB < λA.

B, D

Question. 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

A

Question. Heavy stable nuclei have more neutrons than protons. This is because of the fact that
(a) neutrons are heavier than protons.
(b) electrostatic force between protons are repulsive.
(c) neutrons decay into protons through beta decay.
(d) nuclear forces between neutrons are weaker than that between protons.

B

Question. When an a-particle of mass m moving with velocity v bombards on a heavy nucleus of charge Ze, its distance of closest approach from the nucleus depends on m as
(a) 1/m2
(b) m
(c) 1/m
(d) 1/√m

C

Question. In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. The moderator used have light nuclei. Heavy nuclei will not serve the purpose because
(a) they will break up.
(b) elastic collision of neutrons with heavy nuclei will not slow them down.
(c) the net weight of the reactor would be unbearably high.
(d) substances with heavy nuclei do not occur in liquid or gaseous state at room temperature.

B

Question. The binding energy per nucleon in 37Li and 24He are 7.06 MeV and 5.60 MeV respectively, then in the reaction: p + 73 Li → 2 (24He) the energy of proton must be:
(a) 28.24 MeV
(b) 17.28 MeV
(c) 1.46 MeV
(d) 39.2 MeV

B

Question. Suppose we consider a large number of containers each containing initially 10000 atoms of a radioactive material with a half life of 1 year. After 1 year,
(a) all the containers will have 5000 atoms of the material.
(b) all the containers will contain the same number of atoms of the material but that number will only be approximately 5000.
(c) the containers will in general have different numbers of the atoms of the material but their average will be close to 5000.
(d) none of the containers can have more than 5000 atoms.

C

Question. The variation of decay rate of two radioactive samples A and B with time is shown in figure. Which of the following statements are true?
(a) Decay constant of A is greater than that of B, hence A always decays faster than B.
(b) Decay constant of B is greater than that of A but its decay rate is always smaller than that of A.
(c) Decay constant of A is greater than that of B but it does not always decay faster than B.
(d) Decay constant of B is smaller than that of A but still its decay rate becomes equal to that of A at a later instant.

C, D

Question. Tritium is an isotope of hydrogen whose nucleus Triton contains 2 neutrons and 1 proton. Free neutrons decay into p+er+vr . If one of the neutrons in Triton decays, it would transform into He3 nucleus. This does not happen. This is because
(a) Triton energy is less than that of a He3 nucleus.
(b) the electron created in the beta decay process cannot remain in the nucleus.
(c) both the neutrons in triton have to decay simultaneously resulting in a nucleus with 3 protons, which is not a He3 nucleus.
(d) because free neutrons decay due to external perturbations which is absent in a triton nucleus.

A

Question. In gamma ray emission from a nucleus
(a) only the proton number changes
(b) both the neutron number and the proton number change
(c) there is no change in the proton number and the neutron number
(d) only the neutron number changes

C

Question. A radioactive substance has a half life of four months. Three fourth of the substance will decay in
(a) three months
(b) four months
(c) eight months
(d) twelve months

C

Question. If the end A of a wire is irradiated with α -rays and the other end β is irradiated with b -rays. Then
(a) a current will flow from A to B
(b) a current will flow from B to A
(c) there will be no current in the wire
(d) a current will flow from each end to the mid-point of the wire

A

Question. Which of the following is best nuclear fuel
(a) thorium 236
(b) plutonium 239
(c) uranium 236
(d) neptunium 239

B

Question. In the process of fission, the binding energy per nucleon
(a) increases
(b) decreases
(c) remains unchanged
(d) increases for mass number A < 56 nuclei but decreases for mass number A > 56 nuclei

A

Question. Fusion reaction occurs at temperatures of the order of
(a) 103 K
(b) 107 K
(c) 10 K
(d) 104 K

B

Question. One curie is equal to
(a) 3.7 × 1010 disintegration/sec
(b) 3.2 × 108 disintegration/sec
(c) 2.8 × 1010 disintegration/sec
(d) None of these

A

Question. Nucleus of an atom whose atomic mass is 24 consists of
(a) 11 electrons, 11 protons and 13 neutrons
(b) 11 electrons, 13 protons and 11 neutrons
(c) 11 protons and 13 neutrons
(d) 11 protons and 13 electrons

C

Question. Which of the following nuclear reactions is not possible?

C

Question. If Avogadro number is 6 × 1023, then number of protons, neutrons and electrons in 14 gms of 6C14 are respecitvely
(a) 36 × 1023, 48 × 1023, 36 × 1023
(b) 36 × 1023, 36 × 1023, 36 × 1023
(c) 48 × 1023, 36 × 1023, 48 × 1023
(d) 48 × 1023, 48 × 1023, 36 × 1023

A

Question. 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

C

Question. A gamma ray photon creates an electron-positron pair. If the rest mass energy of an electron is 0.5 MeV and the total kinetic energy of the electron-positron pair is 0.78 MeV, then the energy of the gamma ray photon must be
(a) 0.78 MeV
(b) 1.78 MeV
(c) 1.28 MeV
(d) 0.28 MeV

B

Question. The half-life of radioactive Radon is 3.8 days. The time at the end of which (1/20)th of the Radon sample will remain undecayed is (given log10e = 0.4343)
(a) 13.8 days
(b) 16.5 days
(c) 33 days
(d) 76 days

B

Question. Radioactive element decays to form a stable nuclide, then the rate of decay of reactant is

C

Question. A radioactive nuclide is produced at the constant rate of n per second (say, by bombarding a target with neutrons). The expected number N of nuclei in existence t seconds after the number is N0 is given by

Where l is the decay constant of the sample

C

Question. A radioactive element forms its own isotope after 3 consecutive disintegrations. The particles emitted are
(a) 3 β–particles
(b) 2 β–particles and 1 α–particle
(c) 3 β–particles and 1 α–particle
(d) 2 α–particles and 1 β–particle.

B

Question. If the distance between nuclei is 2 × 10–13 cm, the density of nuclear material is
(a) 3.21 × 10–12 kg/m3
(b) 1.6 × 10–3 kg/m3
(c) 2 × 109 kg/m3
(d) 1 × 1017 kg/m3

D

Question. From the following equations, pick out hte possible nuclear reactions.
(a) 6C13 + 1H1 → 6C14 + 4.3 MeV
(b) 6C12 + 1H1 → 7N13 + 2 MeV
(c) 7N14 + 1H1 → 8O15 + 7.3 MeV
(d) 92U235 + 0n1 → 54X140 + 38Si94 + 20n1 + γ + 200 MeV

B, C

Question. If 200 MeV energy is released in the fission of a single U235 nucleus, the number of fissions required per second to produce 1 kilowatt power shall be (Given 1eV = 1.6 × 10–19 J)
(a) 3.125 × 1013
(b) 3.125 × 1014
(c) 3.125 × 1015
(d) 3.125 × 1016

A

Question. An archaeologist analyses the wood in a prehistoric structure and finds that C14 (Half life = 5700 years) to C12 is only one-fourth of that found in the cells of buried plants. The age of the wood is about
(a) 5700 years
(b) 2850 years
(c) 11,400 years
(d) 22,800 years

C

Question. A heavy nucleus having mass number 200 gets disintegrated into two small fragments of mass number 80 and 120. If binding energy per nucleon for parent atom is 6.5 MeV and for daughter nuclei is 7 MeV and 8 MeV respectively, then the energy released in the decay is X × 110 MeV. Find the value of X.
(a) 3
(b) 4
(c) 2
(d) 1

C

Question. Mp denotes the mass of a proton and Mn that of a neutron. A given nucleus, of binding energy B, contains Z protons and N neutrons. The mass M(N, Z) of the nucleus is given by (c is the velocity of light)
(a) M(N, Z) = NMn + ZMp + B/c2
(b) M(N, Z) = NMn + ZMp – Bc2
(c) M(N, Z) = NMn + ZMp + Bc2
(d) M(N, Z) = NMn + ZMp – B/c2

D

Question. The half life of a radioactive isotope ‘X’ is 50 years. It decays to another element ‘Y’ which is stable. The two elements ‘X’ and ‘Y’ were found to be in the ratio of 1 : 15 in a sample of a given rock. The age of the rock was estimated to be
(a) 150 years
(b) 200 years
(c) 250 years
(d) 100 years

B

Question. If the nuclear radius of 27Al is 3.6 fermi, the approximate nuclear radius of 64Cu in fermi is
(a) 2.4
(b) 1.2
(c) 4.8
(d) 3.6

C

Question. Activity of a radioactive sample decreases to (1/3) rd of its original value in 3 days. Then, in 9 days its activity will become
(a) (1/27) of the orginal value
(b) (1/9) of the original value
(c) (1/18) of the original value
(d) (1/3) of the orignal value

A

Question. The decay constant of radium is 4.28 × 10–4 per year. Its half life will be
(a) 2000 years
(b) 1240 years
(c) 63 years
(d) 1620 years

D

#### Fill in the Blanks

Question. The process responsible for energy production in the sun is _________________.

nuclear fusion

Question. A radioactive isotope of silver has half life of 20 minutes. The fraction of the original activity that remain after one hour is _________________.

1/8

Question. In both the processes of nuclear fission an nuclear fusion, a certain mass disappears. This is called _________________.

mass defect

Question. One atomic mass unit is defined as _________________ of mass of an atom of 6C12.

1/12th

Question. The rest mass of a nucleus is _________________ than the sum of the rest masses of its constituent nucleons.

less

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

same atomic number

Question. Isotones are the nuclides which contains _________________.

same number of neutrons

Question. The Apsara reactor at the Bhabha Atomic Research Centre (BARC), Mumbai, uses _________________ as moderator.

water

Question. Isobars are the atoms of different element which have same _________________ but different atomic number.