Solution :
$\large\frac{1}{\lambda}$$=109678 \bigg[\large\frac{1}{n_1^2}-\frac{1}{n_2^2}\bigg]$
$\qquad= 109678 \bigg[\large\frac{1}{(1)^2}-\frac{1}{\infty}\bigg]$
$\lambda= \large\frac{1}{109678}$$cm=9.1 \times 10^{-6}\;cm$
$\qquad= 9.1 \times 10^{-8}m =91\;nm$
$E= \large\frac{hc}{\lambda}=\frac{6.63 \times 10^{-34}\;J.s \times 3 \times 10^8\;ms^{-1}}{9.1 \times 10^{-8}\;m}$
$E= 2.186 \times 10^{-18}\;J$