What is used as a moderator in a nuclear reactor?

Mention the disadvantages of the nuclear reactor.

How much energy is produced by the fission of $1\, kg$ of uranium?

If the binding energy per nucleon for a deuteron is $1.112 \, MeV$ and for an $\alpha$-particle is $7.07 \, MeV$,then for the reaction $2 \, (_1H^2) \rightarrow _2He^4 + Q$,the value of $Q$ is .......... $MeV$.

When $^{235}_{92}U$ is bombarded with one neutron,fission occurs and the products are three neutrons,$^{94}_{36}Kr$ and:

The energy released by the fission of a single uranium nucleus is $200 \,MeV$. The number of fissions of uranium nucleus per second required to produce $16 \,MW$ of power is (Assume efficiency of the reactor is $50\%$).