Question

When an electron in hydrogen spectrum jumps from $n=7$ to $n=2$, the total number of spectral lines possible are:

• A. $21$
• B. $15$
• C. $5$
• D. $9$

Answer 1

The correct option is B $15$

When an electron in hydrogen spectrum jumps from $n_2$ to $n_1$, the total number of spectral lines possible are

$\frac{(n_2-n_1)(n_2-n_1+1)}{2}$
When an electron in hydrogen spectrum jumps from $n=7$ to $n=2$, the total number of spectral lines possible are

$\frac{(7-2)(7-2+1)}{2}=$ 15

Thus, the correct option is $B$