Fusion reaction is initiated with the help of

Fusion reaction takes place at high temperature because

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.

Under certain circumstances,a nucleus can decay by emitting a particle more massive than an $\alpha$-particle. Consider the following decay processes:
$_{88}^{223} Ra \rightarrow _{82}^{209} Pb + _{6}^{14} C$
$_{88}^{223} Ra \rightarrow _{86}^{219} Rn + _{2}^{4} He$
Calculate the $Q$-values for these decays and determine that both are energetically allowed.

In the nuclear fusion reaction $_1^2H + _1^3H \to _2^4He + n$,given that the repulsive potential energy between the two nuclei is $7.7 \times 10^{-14} \ J$,the temperature at which the gases must be heated to initiate the reaction is nearly? [Boltzmann's constant $k = 1.38 \times 10^{-23} \ J/K$]

$A$ $\pi^0$ meson at rest decays into $2$ $\gamma$ rays: $\pi^0 \to \gamma + \gamma$. Which of the following must happen?