Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R): Assertion (A): Nuclear fission occurs rapidly in atomic bomb explosion and occur relatively slowly in a nuclear reactor. Reasons (R): Nuclear reaction of splitting a massive nucleus into less stable and less massive nuclei with release of energy is nuclear fission. In the light of the above Statements, choose the correct answer from the options given below: