The wavelength of light emitted from second orbit to first orbits in a hydrogen atom is

$1.215 × 10^{-7}$ m $1.215 × 10^{-5}$ m $1.215 × 10^{-4}$ m $1.215 × 10^{-3}$ m

$1.215 × 10^{-7}$ m

Energy radiated $E=10.2 ~eV=10.2 \times 1.6 \times 10^{-19}$ J $\Rightarrow E=\frac{h c}{\lambda} \Rightarrow \lambda=1.215 \times 10^{-7}$ m