Question:
The wavelength of the photon emitted by a hydrogen atom when an electron makes a transition from $n=2$ to $n=1$ state is:
Correct Option: 4,
Solution:
(4)
$\Delta \mathrm{E}=10.2 \mathrm{eV}$
$\frac{\mathrm{he}}{\lambda}=10.2 \mathrm{ev}$
$\lambda=\frac{h c}{(10.2) e}$
$=\frac{12400}{10.2} \mathrm{~A}$
$=121.56 \mathrm{~nm}$
$\simeq 121.8 \mathrm{~nm}$