The main source of solar energy is

Assertion: Heavy water is a better moderator than normal water.
Reason: Heavy water absorbs neutrons more efficiently than normal water.

On fission,a $U^{235}$ nucleus releases $3 \times 10^{-11} \, J$ of energy. In a $1 \, GW$ nuclear reactor,$4.2 \%$ of this energy is converted to useful energy. The $U^{235}$ consumed (in grams) in half an hour is closest to (Avogadro number $N_A = 6.023 \times 10^{23}$)

Fission of nuclei is possible because the binding energy per nucleon in them

Fusion reaction takes place at high temperature because

When a slow neutron goes sufficiently close to a ${U^{235}}$ nucleus,then the process that takes place is