Q 12-12-120JEE MainJEE Main 2018 (15 Apr, Shift 1)Medium
The energy required to remove the electron from a singly ionized Helium atom is $2.2$ times the energy required to remove an electron from helium atom. The total energy required to ionize the Helium atom completely is close to
Answer: (C) $79\ \text{eV}$
$\text{He}^+$ is hydrogen-like with $Z = 2$:
$$E_2 = 13.6\,Z^2 = 13.6\times4 = 54.4\ \text{eV}$$
The first ionisation energy of He is
$$E_1 = \frac{54.4}{2.2} \approx 24.7\ \text{eV}$$
Total energy to remove both electrons:
$$E_1 + E_2 \approx 24.7 + 54.4 \approx 79\ \text{eV}$$
Solution by Sreeraj P, M.Sc Physics