Explanation

(b) Acceleration $a \propto \frac{v^{2}}{r}$
Where $v \propto \frac{Z}{n}$ and $r \propto \frac{n^{2}}{Z} \Rightarrow a \propto \frac{Z^{3}}{n^{4}}$
Since both are in ground state $i.e.,n = 1$
So $a \propto Z^{3} \Rightarrow \frac{a_{He^{+}}}{a_{H}} = \left( \frac{Z_{He^{+}}}{Z_{H}} \right)^{3} = \left( \frac{2}{1} \right)^{3} = \frac{8}{1}$