Question

An atom bomb is an example of –
A. Fusion reaction
B. Controlled fission reaction
C. Uncontrolled fission reaction
D. All the above

Answer 1

Hint: Concept of nuclear fission and fusion reaction. An atom bomb is based on a chain reaction like bombarding uranium with neutrons.

Complete step by step answer:
$ \to $Nuclear reaction: Is a reaction in which a stable nucleus of one element changes into a nucleus of another element.
$ \to $Types: It is of two types
(1) Nuclear fusion
(2) Nuclear fission
$ \to $Nuclear fusion in which two smaller nuclei fuse together to form a larger nucleus, releasing a large amount of energy. For example, in hydrogen bombs.
$ \to $Nuclear fission reaction is that in which a heavy nucleus splits up into two smaller nuclei, giving out a large amount of energy for example, in an atom bomb.
Nuclear chain reaction: When a single $_{92}^{235}U$captures a neutron, by fission it produces $2.5$neutrons. These newly produced neutrons further cause the fission of more uranium
     

Nuclei, which further produces more neutrons and so on. Thus a chain is set up as shown in figure.
Uncontrolled chain reaction: If a chain reaction is started in a fissionable material whose mass is greater than certain critical mass, the reaction is accelerated to such a rapid rate that an explosion of whole material occurs within a microsecond, giving out a large amount of energy. Such a chain reaction is an uncontrolled chain reaction which forms the underlying principle of the atomic bombs.
Form above discussion, it is clear that an atom bomb is an example of uncontrolled fission reaction.

So, the correct answer is “Option C”.

Note:
Remember that an atom bomb explodes into smaller particles such as in uranium and neutrons, so it is fission that is breaking into smaller parts type reaction not fusion.