Which of the transitions in hydrogen atom emits a photon of lowest frequency `(n =` quantum number)?

Options

A. `n=2` to `n=1`
B. `n=4` to `n=2`
C. `n=4` to `n=1`
D. `n=4` to `n=3`

Answer

D

Explanation

The energy level digram schematically looks like this. As we move to higher and higher levels, the energy increases, but the energy gap between any two levels decreases. Hence in the transition from `n=4` to `n=3`, energy released will be `E_4-E_1`. And in the transition from `n=2` to `n=1`, energy released is `E_2-E_1`. Now as `E_4-E_3ltE_2-E_1`
`rArrupsilon_43lthupsilon_21rArr upsilon_43ltupsilon_21`.