On average,how many neutrons are released from the fission of a single $U^{235}$ nucleus?

Pick out the correct statements from the following:
$I$. Electron emission during $\beta$-decay is always accompanied by neutrino.
$II$. Nuclear force is charge independent.
$III$. Fusion is the chief source of stellar energy.

What is a nuclear chain reaction? Explain the difficulties and their removal for its successful operation.

Consider the following statements $A$ and $B$. Identify the correct choice in the given answer.
$A$. $p-n, p-p$ and $n-n$ forces between nucleons are not equal and charge dependent.
$B$. In a nuclear reactor,the fission reaction will be in an accelerating state if the value of the neutron reproduction factor $k > 1$.

In any fission process,the ratio $\frac{\text{mass of fission products}}{\text{mass of parent nucleus}}$ is

Solar energy is mainly caused due to