Which of the following is associated with decrease in pKb value of amines?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Increase in basic strength
The basic strength of an amine is measured by its base dissociation constant Kb, and pKb = −log Kb. A smaller pKb means a larger Kb: the amine accepts a proton from water more readily. So a decrease in pKb goes with an increase in basic strength.
Why the other options are incorrect
Option (1) Increase in acidic strength — Incorrect. pKb measures how strong a base is, not an acid; a lower pKb means a stronger base.
Option (3) Better proton donation — Incorrect. Giving a proton is the behaviour of an acid. An amine acts as a base because its nitrogen accepts a proton.
Option (4) Better electron acceptor — Incorrect. An electron pair acceptor is a Lewis acid. Amines have an unshared pair of electrons on nitrogen, so they act as Lewis bases (electron pair donors).
NCERT (2026-27 edition):
9.6 Chemical Reactions – “… Larger the value of Kb or smaller the value of pKb, stronger is the base.”