Nitrogen is gas while phosphorus, arsenic, antimony and bismuth are solid at room temperature because:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Nitrogen form \(p\pi-p\pi\) multiple bond
Because of its small size and high electronegativity, nitrogen can form strong pπ–pπ multiple bonds with itself. It therefore exists as discrete \( \ce{N2} \) molecules (N≡N, bond enthalpy 941.4 kJ mol−1), held together only by weak van der Waals forces, so it is a gas. The heavier elements P, As, Sb and Bi have large, diffuse p orbitals that cannot overlap effectively sideways; they form single bonds (P–P, As–As) and build up larger molecules or extended structures (\( \ce{P4} \), metallic lattices), which are solids.
Why the other options are incorrect
Option (1) N-N single bond is stronger — Incorrect. The N–N single bond is actually weaker than the P–P single bond, because of repulsion between the lone pairs of the small nitrogen atoms.
Option (2) Nitrogen form \(d\pi-p\pi\) bond — Incorrect. Nitrogen has no d orbitals in its valence shell, so it cannot form dπ–pπ bonds (phosphorus can, as in P=O).
Option (3) Nitrogen form \(d\pi-d\pi\) bond — Incorrect. dπ–dπ bonding needs d orbitals on both atoms; nitrogen has none.
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):
Anomalous Properties of Nitrogen – “Nitrogen differs from the rest of the members of this group due to its smaller size, high electronegativity, high ionisation enthalpy and non-availability of d orbitals. Nitrogen has unique ability to form pπ-pπ multiple bonds with itself and with other elements having small size and high electronegativity (e.g., C, O). Heavier elements of this group do not form pπ-pπ bonds as their atomic orbitals are so large and diffuse that they cannot have effective overlapping.”