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Per NCERT §3.6, helium has electronic configuration 1s² (s-block) but is placed in Group 18 (p-block, noble gases). Why?
ABy historical accident with no justification
BBecause it is the lightest element
CBecause it is radioactive
DBecause it has a completely filled valence shell and behaves like the other noble gases
Answer & Solution
Correct answer: D. Because it has a completely filled valence shell and behaves like the other noble gases
Per NCERT §3.6, He is technically s-block but placed in Group 18 due to its full valence shell + chemical inertness — true noble-gas behaviour.
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