Question

An atom bomb is based on the principle of
A. Nuclear fission
B. Nuclear fusion
C. The liquid drop model
D. None of these

Answer 1

Hint: Nuclear fission is breaking of atoms and nuclear fusion is joining atoms. An atom bomb needs a rapid reaction rate and exothermic reaction. The atomic reaction should trigger other atoms to go through the same. So, it needs a chain reaction. Compare the two types of atomic reactions to determine which one is best for an atom bomb.

Complete step by step answer:
We should start with the definition of nuclear fusion and fission.

Nuclear Fusion:
Nuclear fusion is an atomic reaction in which two or more atoms combine with each other and form one or more atoms having larger numbers of nucleons. The following reaction is an example of Nuclear Fusion reaction.
${}_{1}{{H}^{2}}+{}_{1}{{H}^{2}}\to {}_{2}H{{e}^{4}}+{}_{0}{{n}^{1}}$

Here, the mass difference between the left-hand side and the right-hand side is responsible for the release and absorption of energy. The mass difference contributes to the binding energy of the molecule and makes the resultant molecule stable.

Nuclear Fission:
Nuclear fission is an atomic reaction where an unstable atom disintegrates into one or more smaller atoms. This reaction produces a large amount of energy due to the stability of the new atoms. Above that, it produces gamma photons which starts a chain reaction. That is why, atom bomb uses this principle. The rapid reaction produces a large amount of heat in no time and has devastating effects. One example is:
${}_{92}{{U}^{235}}+{}_{0}{{n}^{1}}\to {}_{56}B{{a}^{144}}+{}_{36}B{{a}^{89}}+3{}_{0}{{n}^{1}}$
Hence, the correct choice is (A).

Note: In the final days of World War II, the atomic bombs were made using the nuclear fission principle. But now, the nuclear power has shifted towards the hydrogen bomb, which uses the Nuclear fusion principle. However, the devastating effect of these bombs were discovered later.
You need to go through each option carefully and know the definition of each. This will help in discarding the confusing options.