Q.Write the reason for the anomalous behaviour of Nitrogen.

Step 1. Small atomic size.

Nitrogen has the smallest atomic radius in Group 15 (1.55 Å versus phosphorus's 1.80 Å and much larger values for the heavier members), so its bonding, hydration and lattice energies differ significantly from the rest of the group.

Step 2. High electronegativity.

Nitrogen is far more electronegative than phosphorus and the heavier members, giving its compounds (like ammonia and the nitrogen oxides) markedly different polarity and hydrogen-bonding behaviour than the corresponding phosphorus compounds.

Step 3. Absence of d orbitals.

Being a period-2 element, nitrogen has no accessible d orbitals in its valence shell, so unlike phosphorus (which readily forms 5-coordinate species such as PCl5 and PF5), nitrogen can never expand its octet beyond four electron pairs and cannot form an analogous NCl5.

Step 4. Multiple-bond-forming ability.

Nitrogen's small size allows efficient sideways (π) overlap of its 2p orbitals, letting it form strong pπ-pπ multiple bonds with itself (as in N≡N) and with other small atoms (as in N=O, N=N in the various nitrogen oxides), a capability phosphorus and the heavier congeners lack — they instead favour single P-P bonds and catenated structures such as the P4 tetrahedron.

Step 5. Combine. …

List and briefly justify each of the standard four reasons (size, electronegativity, d-orbital availability, multiple-bond capability) that make the first member of a p-block group behave differe …

Giving only one reason (commonly just 'small size') instead of the full, interconnected set of size/electronegativity/no-d-orbitals/pπ-pπ-bondin …