$\text { K.E. }=\frac{{n}^{2} {~h}^{2}}{8 \pi^{2} {mr}^{2}} \quad=\frac{4 {~h}^{2}}{8 \pi^{2} {~m}\left(4 {a}_{0}\right)^{2}}$
$\quad\quad\quad\quad\quad\quad\quad\quad=\left(\frac{4}{8 \pi^{2} \times 16}\right) \frac{{h}^{2}}{{ma}_{0}^{2}}$
$\Rightarrow {x}=315.507$
$\Rightarrow 10 {x}=3155 \text { (nearest integer) }$
(આપેલું છે : ઈલેકટ્રોનનું દળ $=9.1 \times 10^{-31} \,kg$, પ્લાન્ક અચળાંક $h =6.63 \times 10^{-34}\, Js$ )
$(h\, = 6.625\times10^{-34}\, J\,s,\, c\, = 3\times10^8\, m\,s^{-1})$