Which among the following is the strongest base in aqueous medium:

The correct answer is Option (2) → (CH₃)₂NH

An amine is basic because the lone pair on nitrogen can accept a proton. Anything that makes this lone pair more available increases basic strength; anything that pulls it away decreases it:

• Alkyl groups (+I effect) push electrons towards nitrogen and increase basicity. In water, solvation of the protonated amine also matters, and for methyl amines the observed order is \( \ce{(CH3)2NH} \) > \( \ce{CH3NH2} \) > \( \ce{(CH3)3N} \) > \( \ce{NH3} \).

• Electron withdrawing groups such as –CN pull electron density away from nitrogen and decrease basicity.

• In aryl amines the lone pair is delocalised into the benzene ring, so it is much less available.

So the strongest base in aqueous medium is (CH₃)₂NH.

Why the other options are incorrect

• Option (1) CH₃NH₂ — Incorrect. It has only one +I methyl group, so it is a little weaker than dimethylamine.

• Option (3) NCCH₂NH₂ — Incorrect. The –CN group withdraws electrons from nitrogen and makes the amine a much weaker base.

• Option (4) C₆H₅NHCH₃ — Incorrect. Resonance with the benzene ring takes the lone pair away from nitrogen, so it is weaker than any of the aliphatic amines.

NCERT (2026-27 edition):
Chemical Reactions – …

Note: The same/similar question has been asked in different years by NTA as per the details given below: