Explanation

(d) Kinetic energy of electron
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ K\ = \frac{{Ze}^{2}}{8\pi\varepsilon_{0}r}$
Potential energy of electron
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ U\ =$ $\frac{1}{4\pi\varepsilon_{0}r}\frac{{Ze}^{2}}{r}$
$\therefore$ Total energy
$E\ = \ K\ + U\ =$ $\frac{{Ze}^{2}}{8\pi\varepsilon_{0}r} - \ \frac{{Ze}^{2}}{4\pi\varepsilon_{0}r}$
Or $\ \ \ \ \ \ \ \ \ \ \ \ \ E =$ $\frac{{Ze}^{2}}{8\pi\varepsilon_{0}r}$
Or $\ \ \ \ \ \ \ \ \ \ \ \ \ \ E = - K$
Or $\ \ \ \ \ \ \ K = - E = \ - ( - 3.4)$
Or $\ \ \ \ \ \ \ \ \ \ \ \ \ \ = 3.4\ eV$