Question

The largest wavelength in the ultraviolet region of the hydrogen spectrum is $122 \,nm$. The smallest wavelength in the infrared region of the hydrogen spectrum (to the nearest integer) is

• A. $802\, nm$
• B. $823\, nm$
• C. $1882\, nm$
• D. $1648\, nm$

Answer 1

Answer: (B)

$823\, nm$

Answer 2

The series in U-V region is Lymen series. Longest wavelength corresponds to minimum energy which occurs in transition from n = 2 to n = 1. ...(i)
The smallest wavelength in the infrared region corresponds to maximum energy of Paschen series.
$\therefore \lambda= \frac{1}{R}$...(ii)
Solving Eqs. (i) and (ii), we get
$\lambda=823.5 nm$