21) The unit of radioactivity is:

a) Rutherford.
b) Becqurel
c) Curie
d) All of these.

ANSWER : All of these.

22) a- particles cannot pass through thick sheets of metals because:

a) They are heavy particles.
b) They have low penetrating power.
c) They have high penetrating power.
d) Both a and b.

ANSWER : Both a and b.

23) Which among the following is a false statement about artificial radioactivity?

a) It is a non-spontaneous process.
b) Less amount of energy is evolved.
c) Projectiles are not required.
d) It can be controlled.

ANSWER : Projectiles are not required.

24) A rock contains 0.257 mg of lead -206 for energy milligram of uranium -238. Half-life period of U²³⁸ is 4.5 x 10⁹ years. What is the age of the rock?

a) 1.8 x 10⁹ years.
b) 2.8 x 10⁹ years.
c) 1.7 x 10⁹ years.
d) 2.6 x 10⁹ years.

ANSWER : 1.7 x 10⁹ years.

25) Find the age of wood, if an old piece of wood has 25.6% as much C¹⁴ as ordinary wood today has. Half-life period of C¹⁴ is 5760 years.

a) 11329 years.
b) 11275 years.
c) 11289 years.
d) 11212 years.

ANSWER : 11329 years.

26) The role of heavy water in a nuclear reactor is:

a) As a moderator.
b) As a coolant.
c) Both a and b
d) None of these.

ANSWER : Both a and b

27) Nuclear fusion takes place at:

a) Low temperature.
b) Moderate temperature.
c) Very high temperature.
d) Both a and b is possible.

ANSWER : Very high temperature.

28) One gram of radium is known to emit 3.7 x 10¹⁰ particles per second. The atomic mass of radium is 226. The half-life period of radium is:

a) 1582 years.
b) 1582.3 years.
c) 1582.7 years.
d) 1582.5 years.

ANSWER : 1582.5 years.

29) An a- particle is emitted from the atom of ₉₂U²³⁸. What is the number of neutrons left in the atom?

a) 140
b) 144
c) 150
d) 156

ANSWER : 144

30) Artificial transmutation can be carried out by particles such as:

a) Protons
b) Deutrons
c) Neutrons
d) All of these.

ANSWER : All of these. 

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