The ratio of the energies of the electron in the hydrogen atom in the first and second excited states is

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