In a nuclear reactor,heavy nuclei are not used as moderators because:

In the proton-proton cycle in the Sun,the energy released when an electron and its antiparticle combine is $\qquad$ .

The fission of a $_{92}U^{235}$ nucleus releases $200 \, MeV$ of energy. Find the rate of fission of $_{92}U^{235}$ required to operate a reactor at a constant power of $5 \, W$.

Which of the following statement$(s)$ is/are correct?
$(1)$ The rest mass of a stable nucleus is less than the sum of the rest masses of its constituent nucleons.
$(2)$ The rest mass of a stable nucleus is greater than the sum of the rest masses of its constituent nucleons.
$(3)$ Nuclear fusion involves the fusion of two light nuclei to form a heavier nucleus.
$(4)$ Nuclear fission involves the release of energy by the splitting of a heavy nucleus.

The operation of a nuclear reactor is said to be critical when the value of the neutron multiplication factor $K$ is:

The source of the Sun's energy is