Which equation represents a fission reaction?

Correct Option B i.e. 235 92U + 1 0n→ 140 55Cs + 94 37Rb + 2 (1 0n)

Reason:
Nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of a heavy atom splits into smaller atoms. During this process, large amount of heat is given out. 

This condition of nuclear fission reaction is satisfied only by option B. 

Rest all the available options are example of nuclear transmutation reactions.

D)can be increased in a closed system

Hope the image of the frequency formula