Answer
$-3.4\;eV$
Work Step by Step
In the figure 39-21 A dot plot showing the volume probability density for the hydrogen atom in the quantum state with $n=2, l=0$ and $m_{l}=0$.
Therefore, the energy of the hydrogen-atom electron corresponds to $n=2$ level is given by
$E_2=-\frac{13.6}{n^2}\;eV=-\frac{13.6}{2^2}\;eV=-3.4\;eV$
