In a sample of $\mathrm{H}$-atom electrons make transition from 5 th excited state to ground state, producing all possible types of photons, then the number of lines in the infrared region are :

The electron is in the fifth excited state, or n=6.

Here transition from

$\begin{array}{r}\mathrm{n}=6\to \mathrm{n}=1\\ \mathrm{n}=5\to \mathrm{n}=1\\ \mathrm{n}=4\to \mathrm{n}=1\\ \mathrm{n}=3\to \mathrm{n}=1\\ \mathrm{n}=2\to \mathrm{n}=1\end{array}$

in the Lyman series" (ultraviolet range)

$\begin{array}{r}\mathrm{n}=6\to \mathrm{n}=2\\ \mathrm{n}=5\to \mathrm{n}=2\\ \mathrm{n}=4\to \mathrm{n}=2\\ \mathrm{n}=3\to \mathrm{n}=2\end{array}$

in the Balmer series (visible range).
While

$\begin{array}{r}\mathrm{n}=6\to \mathrm{n}=3\\ \mathrm{n}=5\to \mathrm{n}=3\\ \mathrm{n}=4\to \mathrm{n}=3\\ \mathrm{n}=6\to \mathrm{n}=4\\ \mathrm{n}=5\to \mathrm{n}=4\\ \mathrm{n}=6\to \mathrm{n}=5\end{array}$

These changes occur in the infrared area.