In a hydrogen atom, the electron and proton are bound at a distance of about 0.53 Å: Estimate the potential energy of the system in eV, taking the zero of the potential energy at infinite separation of the electron from proton.

Question

$\begin{array}{1 1} -27.2\;ev \\0.7\;ev \\ 0.4\;ev \\ 0.9\;ev\end{array}$