The largest wavelength in the ultraviolet region of the hydrogen spectrum is `122nm`. The smallest wavelength in the infrared region of the hydrogen spectrum (to the nearest interger) is (a) `802nm` (b) `823nm`
(c ) `1882nm` (d) `1648nm`.

Options

A. 802 nm
B. 823 nm
C. 1882 nm
D. 1648 nm

Answer

B

Explanation

The series in uv region is Lyman series. Longest wavelength corresponds to minimum energy which occurs in transition from `n =2` to `n =1`
`:. 122 = (1//R)/((1)/(1^(2)-(1)/(2^(2))` ….(1)
The smallest wavelength in the infrared region corresponds to maximum energy of paschen series.
`lamda = (1//R)/((1)/(3^(2))-(1)/(infty))`....(2)
from (1) and (2) `lamda = 823.5 nm`.