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 :
Correct Option: , 4
Solution:
$\frac{1}{\lambda}=\mathrm{R}\left(\frac{1}{1^{2}}-\frac{1}{2^{2}}\right)$
$\lambda=121.8 \mathrm{~nm} .$