Answer
Main group = elements whose valence shell involves only s or p subshells (Groups 1–2, 13–18).
- Configuration A (
[Ne] 3s¹
) corresponds to Na, an s-block metal. - Configuration C (
[Kr] 4d10 5s2 5p5
) is I (iodine), a p-block halogen.
Configurations B and D possess 3d electrons, and E (Th) has 6d/5f involvement — so none are main-group.
Therefore, the only main-group configurations listed are A and C, making Option 2 the correct choice.