Concept:For molecular solids in the p-block, melting and boiling points depend heavily on the strength of intermolecular London dispersion forces (a type of van der Waals force), which scale with molecular mass and size.
Solution:- Phosphorus exists naturally as a tetra-atomic molecule: \( \text{P}_4 \).
- Sulphur exists naturally as an octa-atomic puckered ring molecule: \( \text{S}_8 \).
- Because an \( \text{S}_8 \) molecule is physically much larger and contains twice as many atoms/electrons as a \( \text{P}_4 \) molecule, it is far more polarizable.
- This massive electron cloud creates much stronger van der Waals forces between the sulphur molecules compared to phosphorus.
- Stronger intermolecular forces require more thermal energy to break, giving Sulphur a higher melting point.
Why other options are incorrect:- Option B is factually inverted. Options C & D attempt to frame the answer around phosphorus, but the relative comparison clearly points to the larger van der Waals forces in Sulphur as the primary driving factor.
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