Molecules are constituent particles of molecular solids. Identify the molecular solid amongst the following:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(SO_2\)
Crystalline solids are classified by the particles at the lattice points and the forces between them:
Molecular solids — molecules held by van der Waals forces, dipole–dipole forces or hydrogen bonds (Ar, \( \ce{CCl4} \), solid \( \ce{SO2} \), solid \( \ce{NH3} \), ice).
Ionic solids — ions held by Coulombic forces (NaCl, MgO).
Metallic solids — positive metal ions in a sea of free electrons (Fe, Cu).
Covalent or network solids — atoms joined by covalent bonds through the whole crystal (diamond, graphite, \( \ce{SiO2} \)).
\( \ce{SO2} \) is a discrete, bent, polar molecule; in the solid its molecules are held by dipole–dipole forces. So solid \( \ce{SO2} \) is a polar molecular solid.
Why the other options are incorrect
Option (2) C — Incorrect. Carbon (diamond or graphite) is a covalent network solid; there are no separate molecules, only one giant network of C–C bonds.
Option (3) Fe — Incorrect. Iron is a metallic solid; Fe ions are held together by a sea of delocalised electrons.
Option (4) NaCl — Incorrect. Sodium chloride is an ionic solid made of \( \ce{Na^{+}} \) and \( \ce{Cl^{-}} \) ions held by Coulombic forces.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Molecular Solids
