JEE Main · 2025 · Shift-IeasyPB12-129

The large difference between the melting and boiling points of oxygen and sulphur may be explained on the basis of: (a)…

p-Block Elements (Class 12) · Class 12 · JEE Main Previous Year Question

Question

The large difference between the melting and boiling points of oxygen and sulphur may be explained on the basis of:

(a) Atomic size \quad (b) Atomicity \quad (c) Electronegativity \quad (d) Electron gain enthalpy

Options
  1. a

    Atomic size

  2. b

    Atomicity

  3. c

    Electronegativity

  4. d

    Electron gain enthalpy

Correct Answerb

Atomicity

Detailed Solution

Key concept — Atomicity:

  • Oxygen: O2\text{O}_2 (atomicity = 2, diatomic molecule)
  • Sulphur: S8\text{S}_8 (atomicity = 8, crown-shaped ring)

Effect on melting/boiling points:

The larger the molecule, the stronger the van der Waals (London dispersion) forces.

S8\text{S}_8 has a much larger molecular mass and surface area than O2\text{O}_2:

  • M(O2)=32g/molM(\text{O}_2) = 32\,\text{g/mol}
  • M(S8)=256g/molM(\text{S}_8) = 256\,\text{g/mol}

This leads to significantly stronger intermolecular forces in sulphur → much higher melting point (113°C113°\text{C}) and boiling point (445°C445°\text{C}) compared to oxygen (mp = 219°C-219°\text{C}, bp = 183°C-183°\text{C}).

The large difference is due to atomicity (S₈ vs O₂).

Answer: (b) Atomicity

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