In the following nuclear reaction $X$ is

$$ { }_{13} \mathrm{Al}^{27}+{ }_2 \mathrm{He}^4 \longrightarrow{ }_0 n^1+X $$

Nuclear fission and fusion can be explained on the basis of

If $F_1, F_2$ and $F_3$ are the relative strengths of the gravitational, the weak nuclear and the electromagnetic forces respectively, then

If an electron is moving in the 4th orbit of the hydrogen atom, then the angular momentum of the electron in SI unit is