Complete the equation for the following fission process:
$_{92}U^{235} + _0n^1 \to _{38}Sr^{90} + ....$

Heavy water is used as a moderator in a nuclear reactor because

How much energy is released by the fusion of four hydrogen atoms to form a helium nucleus (in $MeV$)?

Suppose a ${ }_{88}^{226} Ra$ nucleus at rest and in the ground state undergoes $\alpha$-decay to a ${ }_{86}^{222} Rn$ nucleus in its excited state. The kinetic energy of the emitted $\alpha$ particle is found to be $4.44 \text{ MeV}$. The ${ }_{86}^{222} Rn$ nucleus then goes to its ground state by $\gamma$-decay. The energy of the emitted $\gamma$-photon is . . . . . . . $\text{keV}$.
[Given: atomic mass of ${ }_{88}^{226} Ra = 226.005 \text{ u}$,atomic mass of ${ }_{86}^{222} Rn = 222.000 \text{ u}$,atomic mass of $\alpha$ particle $= 4.000 \text{ u}$,$1 \text{ u} = 931 \text{ MeV}/c^2$]

If all the helium in a star is converted into oxygen in its core,the energy released per oxygen nucleus is...........$MeV$?
[Mass of $He = 4.0026 \, a.m.u.$,Mass of $O = 15.9994 \, a.m.u.$]

Define the multiplication factor $(k)$ in the context of a nuclear chain reaction.