Question

How many Balmer spectral lines will be obtained when the excited electrons return from 8th shell to 2nd shell?

• A. 21
• B. 4
• C. 10
• D. 15

Answer 1

The correct option is A 21

The general formula for calculating number of spectral lines
= $\frac{(n_H-n_L)(n_H-n_L+1)}{2}$
Here Balmer line means transition from 8th shell to 2nd shell
$n_H=8$, $n_L=2$
$\text{Number of spectral lines}=\frac{(8-2)(8-2+1)}{2}$
$=\frac{\left(6\right)\left(7\right)}{2}$
$=21$