The wavelength of the photon emitted by
Question:

The wavelength of the photon emitted by a hydrogen atom when an electron makes a transition from $\mathrm{n}=2$ to $\mathrm{n}=1$ state is :

1. $194.8 \mathrm{~nm}$

2. $913.3 \mathrm{~nm}$

3. $490.7 \mathrm{~nm}$

4. $121.8 \mathrm{~nm}$

Correct Option: , 4

Solution:

$\frac{1}{\lambda}=\mathrm{R}\left(\frac{1}{1^{2}}-\frac{1}{2^{2}}\right)$

$\lambda=121.8 \mathrm{~nm} .$