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The binding energy of an electron in the ground state of helium is 24.6 eV. What is the total energy required to remove both electrons from a helium atom (in eV)?

1. 54.4 eV
2. 38.2 eV
3. 79.0 eV
4. Insufficient data

Correct answer: 79.0 eV

Solution

The first ionisation energy is given as 24.6 eV. He+ with Z=2 has ionisation energy 13.6 * 4 = 54.4 eV. Total = 24.6 + 54.4 = 79.0 eV.

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