According to the Bohr model, the ground-state energy of a hydrogen atom is:

Bohr's energy formula: $E_n = -\dfrac{13.6}{n^2}$ eV for hydrogen. For the ground state $n = 1$: $E_1 = -13.6$ eV. - Option A ($-3.4$ eV) is $E_2$. - Option D ($-27.2$ eV) is the magnitude of *twice* the ground-state energy (a common confusion with the virial-theorem relation $E = -\frac{1}{2}|U|$).