A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. The number of spectral lines emitted will be:

$\begin{array}{l}\mathrm{n}=4 \mathrm{E}=-0.85\mathrm{eV}\\ \mathrm{n}=3 \mathrm{E}=-1.5\mathrm{eV}\\ \mathrm{n}=2 \mathrm{E}=-3.4\mathrm{eV}\\ \mathrm{n}=1 \mathrm{E}=-13.6\mathrm{eV}\end{array}$
n = 1 to 3   $\mathrm{\Delta E}$=12.1eV
n = 1 to 4   $\mathrm{\Delta E}$=12.75eV
So  n = 3  to 1
Max 3 possibilities $3\to 2, 2\to 1, 3\to 1$