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Nuclei Class 12 MCQs Questions with Answers
Solving the Nuclei Multiple Choice Questions of Class 12 Physics Chapter 13 MCQ can be of extreme help as you will be aware of all the concepts. These MCQ Questions on Nuclei Class 12 with answers pave for a quick revision of the Chapter thereby helping you to enhance subject knowledge. Have a glance at the MCQ of Chapter 13 Physics Class 12 and cross-check your answers during preparation.
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 U235 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 88Ra226 decays in a series by emission of three alpha (α) and a beta (ß) particle, the isotope X which remains undecayed is
(a) 83X214
(b) 84X218
(c) 84X220
(d) 87X223
Answer
Answer: (a) 83X214
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 6C12
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 235U92 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
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