JEE Main 2023 · 11 April · evening · Single correct · +4 / −1
Which one of the following pairs is an example of polar molecular solids?
- (a) HCl(s), AlN(s)
- (b) MgO(s), SO₂(s)
- (c) SO₂(s), NH₃(s)
- (d) SO₂(s), CO₂(s)
Answer and solution
Answer (c) SO₂(s), NH₃(s)
Solution
Chemistry ma’am · 3 steps
Ask two things for each solid: is it made of separate molecules, and is each molecule polar?
- Polar molecular solid. The particles must be separate molecules, not ions or a giant covalent network. Each molecule must also have a net dipole, so neighbours attract by dipole–dipole forces.
Solid Particles Shape and dipole Type of solid HCl molecules H–Cl bond, polar polar molecular AlN atoms in a giant network no separate molecules covalent (network) MgO Mg²⁺ and O²⁻ ions no separate molecules ionic SO₂ molecules bent, dipoles do not cancel polar molecular NH₃ molecules pyramidal, dipoles add up polar molecular (also H-bonded) CO₂ molecules linear, dipoles cancel non-polar molecular - About ammonia. NH₃ molecules are polar, and in the solid they also form hydrogen bonds. Hydrogen bonding is a strong kind of attraction between polar molecules, so NH₃(s) is still a polar molecular solid.
- So. Only (c) has both members as polar molecular solids: bent SO₂ and pyramidal NH₃.
The idea to keep. First check that the solid is built from discrete molecules. Then use the shape: if the bond dipoles cancel, as in linear CO₂, the molecular solid is non-polar.
Answer from the NTA final answer key. Solution by PrepWiser.