JEE Main 2025 · 24 January · morning · Single correct · +4 / −1
The large difference between the melting and boiling points of oxygen and sulphur may be explained on the basis of
- (a) Atomicity
- (b) Electron gain enthalpy
- (c) Atomic size
- (d) Electronegativity
Answer and solution
Answer (a) Atomicity
Solution
Chemistry ma’am · 3 steps
Look at how many atoms sit in each molecule: O₂ has two, S₈ has eight.
- What melting needs. Both elements are molecular. Melting or boiling them only has to overcome the weak van der Waals forces between molecules, not the covalent bonds inside them.
- Why atomicity differs. The small oxygen atom forms a strong pπ–pπ double bond, so it stays as O₂. Sulphur is larger, so it prefers single bonds and links up into puckered S₈ rings.
Property Oxygen Sulphur Molecule O₂, diatomic S₈, octatomic Size of molecule small large, many electrons van der Waals forces weak much stronger State at room temperature gas solid - So. The bigger S₈ molecule has far stronger intermolecular forces, so sulphur melts and boils much higher than oxygen. The difference is explained by atomicity, option (a).
The idea to keep. For molecular elements, melting and boiling points follow the size of the molecule. More atoms per molecule means stronger van der Waals forces and higher melting and boiling points.
Answer from the NTA final answer key. Solution by PrepWiser.