The ionization enthalpy of lithium is much lower than that of helium despite the fact that the nuclear charge of lithium is +3 and that of helium is +2. It is due to:

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2s electron in lithium is more strongly bound to the nucleus than the ls electron in He

2s electron in lithium is equally bound to the nucleus than the ls electron in He

2s electron in lithium is less strongly bound to the nucleus than the ls electron in H

Atomic size of He is more than Li

answer is C.

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Detailed Solution

The ionization enthalpy of lithium is much lower than that of helium .Because 2s electron in lithium is less strongly bound to the nucleus than the ls electron in H.

The force of repulsion between electrons and the nucleus, as well as the force of attraction between them, affect the ionization enthalpy.

Compared to helium, the nucleus of lithium exhibits a substantially less force of attraction for electrons.
Lithium's ionization enthalpy is therefore significantly smaller than helium's.

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