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
`lambda=(1//R)/((1)/(3^(2))-(1)/(oo))`.....(2)
from (1) and (2) `lambda=823.5 nm.`