The ionisation energy of hydrogen atom is 13.6 eV, the ionisation

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The ionisation energy of hydrogen atom is 13.6 eV, the ionisation energy of helium atom would be

1. 13.6 eV
2. 27.2 eV
3. 6.8 eV
4. 54.4 eV

Correct Option: D

E ∝ Z² and Z for helium = 2
∴ (E)_He = 4 × 13.6 = 54.4 eV