15 eV is given to electron in 4th orbit, then find its final energy when it comes out of H-atom [AIIMS 2019]

Total energy given to electron in 4th orbit, E = 15 eV
Energy of nth orbit of H-atom,

$E\text{'}=-\frac{13.6}{n^2}eV$

So, energy of 4th orbit of H-atom,  $E\text{'}=\frac{-13.6}{4^2}=-0.85\mathrm{eV}$

$\therefore$  Ionisation energy of 4th orbit  $= \left|-E\text{'}\right|$

 $= \left|-0.85 \mathrm{eV}\right| = 0.85 \mathrm{eV}$

Thus, final energy of the electron, when it comes out of H-atom,
E = Total energy given to electron-Ionisation energy of 4th orbit.
= 15 $-$ 0.85 = 14.15 eV