Question

The ionisation energy of hydrogen atom is \(13.6\mathrm{eV}\). What will be the ionisation energy of He\(^+\)?

• A. \(13.6\mathrm{eV}\)
• B. \(54.4\mathrm{eV}\)
• C. \(122.4\mathrm{eV}\)
• D. Zero

Hint:

Formula: \(E_n = -13.6 \times \frac{Z^2}{n^2}\) eV. Ionisation energy is \(|E_1|\).

Answer 1

The Correct Option is B

Step 1: Underlying Concept:
For hydrogen-like species, Ionisation Energy (IE) \(\propto Z^2\).
Step 2: Explanation:
IE for H (Z=1) is 13.6 eV. For He\(^+\) (Z=2), IE = \(13.6 \times (2)^2 = 13.6 \times 4 = 54.4 \mathrm{eV}\).
Step 3: Conclusion:
54.4 eV