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Per NCERT §3.7.1(d), why do NOBLE GASES have LARGE POSITIVE electron gain enthalpies (e.g. He +48, Ne +116 kJ/mol)?
AThey have very large atomic radii
BTheir nuclei repel electrons
CNoble gases have no orbitals
DThe added electron must enter the NEXT principal quantum level — energetically very unfavourable for a closed-shell atom
Answer & Solution
Correct answer: D. The added electron must enter the NEXT principal quantum level — energetically very unfavourable for a closed-shell atom
Per NCERT §3.7.1(d) + Table 3.7, closed-shell noble gas + adding e⁻ requires occupation of the next shell → +ve (endothermic) ΔₑgH.
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