Question

A certain electronic transition from an excited state to the ground state of the $H$ atom in one or more steps gives rise to four lines in the ultraviolet region of the spectrum, how many lines does this transition produce in the infrared region of the spectrum.

• A. $1$
• B. $2$
• C. $3$
• D. $4$

Answer 1

The correct option is C $3$

Let the four lines are observed in the ultraviolet region of the spectrum.

These correspond to the transitions

$5\to 1,4\to 1,3\to 1$ and $2\to 1$

The possible transitions in the IR region are

$5\to 4,5\to 3$ and $4\to 3$

Therefore the infrared region of the spectrum, $3$ lines are produced.

Hence, te correct option is $\text{C}$