Choose the correct statements from the following:
A. I is more basic than II
B. II is more basic than I and III
C. III is more basic than II.
D. All behave as Lewis bases.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B and D only
Basicity depends on how freely the lone pair on nitrogen is available for a proton. In pyridine the lone pair sits in an sp2 orbital in the plane of the ring and is not part of the aromatic sextet, so it is available (pKb ≈ 8.8). In aniline the lone pair is delocalised into the benzene ring by resonance, so it is less available (pKb = 9.38). In pyrrole the lone pair is one of the six π electrons of the aromatic ring; protonating it would destroy the aromaticity, so pyrrole is hardly basic at all. Order of basicity: pyridine (II) > aniline (III) > pyrrole (I).
A. I is more basic than II — Incorrect. Pyrrole is far less basic than pyridine, because its lone pair is tied up in the aromatic sextet.
B. II is more basic than I and III — Correct. Pyridine’s sp2 lone pair is free, so it is the strongest base of the three.
C. III is more basic than II. — Incorrect. Resonance delocalisation makes aniline weaker than pyridine.
D. All behave as Lewis bases. — Correct. Each has an unshared pair of electrons on nitrogen that it can donate, which is what makes a Lewis base.
Note: The question is from beyond the NCERT textbook.
NCERT (2026-27 edition):
Basic Character of Amines – “… Amines have an unshared pair of electrons on nitrogen atom due to which they behave as Lewis base.”