Answer the question on the basis of passage given below:
Second period elements of p-Block differ from the rest of their group members due to their small atomic size, high electronegativity, high ionization enthalpy and absence of d-orbitals.
The elements from the second period like C, N, O have unique property of forming pπ–pπ multiple bonds whereas other heavier elements of p-block form dπ–pπ multiple bonds. This changes the properties of second period elements to great extent. Also the single bond strength of the p-block elements with their own atoms gets affected by their atomic size and presence of lone pairs.
Inert pair effect also affects the properties of the p-Block elements especially for those elements which are present from 4th period onward and this happens due to poor screening effect of inner (n–1)d subshell electrons.
Phosphorus forms \(PF_5\) but nitrogen cannot form \(NF_5\) as:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Nitrogen cannot extend its octet due to absence of d-orbitals in it
In \( \ce{NF5} \) nitrogen would need five bonds, i.e. ten electrons around it. Nitrogen has only four orbitals (one 2s and three 2p) in its valence shell and no d orbitals, so its covalency is restricted to a maximum of 4. Phosphorus has vacant 3d orbitals, so it can expand its covalency beyond four, as in \( \ce{PF5} \).
Why the other options are incorrect
Option (1) Small sized nitrogen cannot accommodate five fluorine atoms around it — Incorrect. The limit comes from the number of valence orbitals, not from lack of space around the atom.
Option (2) N–F bond is stronger than P–F bond — Incorrect. The strength of the N–F bond is not the reason; \( \ce{NF3} \) forms readily.
Option (3) Phosphorus is less electronegative than nitrogen — Incorrect. Electronegativity does not decide whether an atom can expand its octet.
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):
Oxidation States and Trends in Chemical Reactivity – …
