Electronic transition in He ion takes from `n_2` to `n_1` shell such that :
`2n_2 + 3n_1 = 18 , 2n_2 - 3n_1 = 6`
What will be the total number of photons emitted when electrons transit to `n_1` shell ?

Options

A. 21
B. 15
C. 20
D. 10

Answer

D

Explanation

`4n_2 = 24 implies n_2 = 6`
`n_1 = 2 ` no. of spectral lines `(4(5))/(2)` = 10