(b) According to Kepler’s 3rd law.
$T^{2} \propto r^{3}$
$\therefore\ \frac{T_{1}}{T_{2}} = \left( \frac{r_{1}}{r_{2}} \right)^{3/2} = 8$
$\frac{r_{1}}{r_{2}} = 8^{2/3} = 4$
According to Bohr atom model, $r \propto n^{2}$
$\therefore\ \frac{n_{1}^{2}}{n_{2}^{2}} = \frac{r_{1}}{r_{2}} = 4;\ \frac{n_{1}}{n_{2}} = 2$
If $n_{1} = 2$, then $n_{2} = 1$