# MCQ Questions for Class 12 Physics Chapter 13 Nuclei with Answers

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## Nuclei Class 12 MCQs Questions with Answers

Question 1.
Beta rays emitted by a radioactive material are
(a) neutral particles.
(b) charged particles emitted by nucleus.
(c) electromagnetic radiations.
(d) electrons orbiting around the nucleus.

Answer

Answer: (b) charged particles emitted by nucleus.

Question 2
How much energy will approximately be released if all the atoms of 1 kg of deuterium could undergo fusion?
(a) 2 × 107 kWh
(b) 9 × 1013J
(c) 6 × 1027 Cal
(d) 8 × 1023 MeV.

Answer

Answer: (b) 9 × 1013J

Question 3.
The packing fraction for $$_{7}^{14}$$N isotope whose mass is 14.003 amu is:
(a) 0.9
(b) 7.8 × 10-3
(c) 1.0002
(d) 2.1 × 10-4

Answer

Answer: (b) 7.8 × 10-3

Question 4.
The binding energy per nucleon is almost constant for many nuclei. It shows that nuclear forces are
(a) Charge independent
(b) saturated in nature
(c) short range in nature
(d) attractive in nature

Answer

Answer: (b) saturated in nature

Question 5.
The binding energies per nucleon for a deutron and an α- particle are x1 and x2 respectively. The energy Q released in reaction
1H² + 1H² → $$_{2}^{4}$$He + Q is
(a) 4 (x1 + x2)
(b) 4 (x1 – x2)
(c) 2 (x1 + x2)
(d) 2 (X1 – x2).

Answer

Answer: (b) 4 (x1 – x2)

Question 6.
The binding energies of the atoms of elements A and B are Ea and Eb respectively. Three atoms of the elements B fuse to give one atom of element A. This fusion process is accompained by release of energy E. Then Ea, Eb and E are related to each other as:
(a) Ea + E = 3 Eb
(b) Ea = 3Eb
(c) Ea – E = 3 Eb
(d) Ea + 3Eb + E = 0

Answer

Answer: (a) Ea + E = 3 Eb

Question 7.
Let mn and mp be the masses of a neutron and a proton respectively. M1 and M2 are the masses of a $$_{10}^{20}$$Ne nucleus and a $$_{20}^{40}$$Ca nucleus respectively. Then
(a) M2 < 2M1
(b) M2 > 2M1
(c) M2 = 2M1
(d) M1 < 10 (mn + mp).

Answer

Answer: (a) and (d).

Question 8.
One requires an energy En to remove a nucleon from a nucleus and an energy Ee to remove an electron from an atom. Then
(a) En = Ee
(b) En > Ee
(c) En < Ee
(d) En > Ee.

Answer

Answer: (b) En > Ee

Question 9.
When the number of nucleons in nuclei increases, the binding energy per nucleon numerically
(a) increases continuously with mass number.
(b) decreases continuously with mass number.
(c) First increases and then decreases with increase of mass number.
(d) Remains constant with mass number.

Answer

Answer: (c) First increases and then decreases with increase of mass number.

Question 10.
For an atomic reactor being critical, the ratio (k) of the average number of neutrons produced and used in chain reaction
(a) depends upon the mass of the fissionable material.
(b) is greater than one.
(c) is less than one.
(d) is equal to one.

Answer

Answer: (a) depends upon the mass of the fissionable material.

Question 11.
Maximum permissible radiation dose a a person may have with no adverse effects is
(a) 250 × 10-1 roentgen’s per week.
(b) 250 × 10-2 roentgen’s per week.
(c) 250 × 10-3 roentgen’s per week.
(d) 250 roentgen’s per week.

Answer

Answer: (c) 250 × 10-3 roentgen’s per week.

Question 12.
For thorium A = 232 and Z = 90. At the end of some radioactive disintegrations we obtain an isotope of lead with $$_{82}^{208}$$pb. Then the number of emitted α and ß particles are
(a) α = 4, ß = 6
(b) α = 5, ß = 5
(c) α = 6, ß = 4
(d) α = 6, ß = 6

Answer

Answer: (c) α = 6, ß = 4

Question 13.
If 10 % of a radioactive material decays in 5 days, then the amount of the original material left after 20 days is nearly.
(a) 60%
(c) 75%
(b) 70%
(d) 66%

Answer

Answer: (d) 66%

Question 14.
If the atomic masses for the parent and daughter element in a radioactive decay are Mp and Md and the mass of the electron me then the Q-value for the radioactive ß decay is given by
(a) Q = Mp
(b) Q = (Mp – Md – Mc) C²
(c) Q = (Mp – Md)C²
(d) Q = (Mp – md – 2Me)C².

Answer

Answer: (c) Q = (Mp – Md)C²

Question 15.
For the fission of heavy nucleus, neutron is more effective than the proton or a particle because
(a) Neutron is heavier than α-particle.
(b) Neutron is lighter than α-particle.
(c) Neutron moves with a small velocity.
(d) Neutron is uncharged.

Answer

Answer: (d) Neutron is uncharged.

Question 16.
Which of the following is the best nuclear fuel.
(a) Thorium-236
(b) Plutonium – 239
(c) Neptunium-239
(d) Uranium-236.

Answer

Answer: (b) Plutonium – 239

Question 17.
The energy released in the fission of a single $$_{92}^{235}$$U nucleus is 200 MeV. The fission rate of $$_{92}^{235}$$U fuelled reactor operating a power level of 5 Watt is
(a) 1.56 × 1014 per sec.
(b) 1.56 × 1017 per sec.
(c) 1.56 × 1020 per sec.
(d) 1.56 × 1017 per sec

Answer

Answer: (b) 1.56 × 1017 per sec.

Question 18.
Heavy water is used as a moderator in a nuclear reactor. The function of the moderator is to
(a) absorb neutrons and stop chain reaction
(b) To cool the reactor
(c) To slow down the neutrons to thermal energies.
(d) To control the energy released.

Answer

Answer: (c) To slow down the neutrons to thermal energies.

Question 19.
The volume of a nucleus is smaller than that of an atom by a factor of:
(a) 10
(b) 105
(c) 1015
(d) 1010

Answer

Answer: (c) 1015

Question 20.
Consider the fission reaction :
$$_{96}^{236}$$U → x117 + Y117 + 0n1 + 0n1
i.e., two nuclei of same mass numbers 117 are formed plus two neutrons. The binding energy per nuclear of X and Y is 8.5 MeV whereas U236 is 7.6 MeV. The total energy liberated will be about:
(a) 2 MeV
(b) 20 MeV
(c) 2,000 MeV
(d) 200 MeV

Answer

Answer: (d) 200 MeV

Question 21.
Fusion reations place at high temp, because
(a) Kinetic energy is high enough to overcome repulsion between nuclei.
(b) Nuclei break up at high temperature.
(c) Atoms are ionised at high temperature.
(d) Molecules break up at high temperature.

Answer

Answer: (a) Kinetic energy is high enough to overcome repulsion between nuclei.

Question 22.
Which of the following nuclei is most stable
(a) even-even
(b) odd-odd
(c) odd-even
(d) even-odd

Answer

Answer: (a) even-even

Fill in the Blanks

Question 1.
Atoms having the same ……………….. but different ……………….. are called isotopes.

Answer

Answer: Atomic number, mass number.

Question 2.
The size of the nucleus varies as ……………….. power of mass number.

Answer

Answer: ($$\frac {1}{3}$$)

Question 3
……………….. is the process in which light nuclei fuse together to form a heavy nucleus.

Answer

Answer: Nuclear fusion.

Question 4.
In the fission of 235U nucleus on an average ……………….. neutrons are released.

Answer

Answer: 2.5.

Question 5.
In a nuclear reactor, heavy water is used as a ……………….. which slows down the neutrons.

Answer

Answer: Moderator.

Question 6.
The difference between $$_{92}^{235}$$U and $$_{92}^{238}$$U is that $$_{92}^{238}$$U contains three more ……………….. and fission of $$_{92}^{238}$$U is caused ……………….. by neutrons while fission of $$_{92}^{235}$$U is caused by ……………….. neutrons.

Answer

Answer: neutrons, fast, slow.

Question 7.
The order of magnitude of the density of nuclear matter is ………………..

Answer

Answer: 1017 kg m-3.

Question 8.
The average binding energy per nucleon for the nuclei lying in the middle of periodic table is nearly ………………..

Answer

Answer: 8.5 MeV.

Question 9.
Two deuterium nuclei can combine to form a ……………….. if they possess sufficiently

Answer

Answer: Helium nucleus, high kinetic energy.

Question 10.
The average energy released per fission of $$_{92}^{235}$$U is approximately ……………….. MeV.

Answer

Answer: 200.

Question 11.
Proton was discovered by ……………….. and neutron was discovered by ………………..

Answer

Answer: Rutherford, Chadwick.

Question 12.
The ratio of the radii of the nuclei 13Al27 and 52Te125 is approximately ………………..

Answer

Answer: 3 : 5.

Question 13
……………….. was the fissionable material used in the bomb dropped at Nagasaki in 1945.

Answer

Answer: Plutonium.

Question 14.
An element A decays into element C by a two step process:
A → B + $$_{2}^{4}$$He
B → C + 2e,
Then A and C are ………………..

Answer

Answer: Isotopes.

Question 15.
The sun obtains its radiant energy from ………………..

Answer

Answer: Fusion process.

Question 16.
The B.E. per nucleon is maximum for ………………..

Answer

Answer: $$_{26}^{56}$$Fe.

Question 17.
Slow neutrons are incident on a sample of uranium containing both $$_{92}^{235}$$U and $$_{92}^{238}$$U isotopes, then only ……………….. atoms will undergo fission. .

Answer

Answer: $$_{92}^{235}$$U

Question 18.
The critical mass of the fissionable material is ………………..

Answer

Answer: The minimum mass needed for chain reaction.

Question 19.
The bulk of energy released in nuclear fission process appears as ………………..

Answer

Answer: Kinetic energy of fission fragments.

Question 20.
In a given reascion:
$$_{Z}^{A}$$X → $$_{Z+1}^{A}$$Y → $$_{Z-1}^{A-4}$$K → $$_{Z-1}^{A-4}$$K
the radioactive radiations are emitted in.the sequence of ………………..

Answer

Answer: ß, α, γ.

Question 21.
A positron has the same mass as ………………..

Answer

Answer: electron.

Question 22.
Neutrino is a particle with ………………..

Answer

Answer: Chargeless property and has spin.

Question 23.
Out of α, ß and γ radiations, ……………….. and ……………….. are affected by a magnetic field.

Answer

Answer: Alpha (α) and, beta (ß) radiations.

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