Arrange the following amines in increasing order of basicity in aqueous solution

(A) $(CH_3)_2NH$
(B) $CH_3NH_2$
(C) $(CH_3)_3N$
(D) $NH_3$

Choose the correct answer from the options given below.

(D), (C), (B), (A)

The correct answer is Option (4) → (D), (C), (B), (A)

Basicity of amines in aqueous solution depends on:

• +I effect of alkyl groups
• Hydration (solvation) of the protonated amine — this stabilizes the conjugate acid.

General order in aqueous medium:

$\text{Secondary amine} > \text{Primary amine} > \text{Tertiary amine} > \text{Ammonia}$

Reason:

• Secondary amines are most basic due to strong +I effect + good hydration.
• Tertiary amines are less hydrated, so they become less basic than primary in water.

Given amines:

(A) (CH₃)₂NH → secondary amine → most basic
(B) CH₃NH₂ → primary amine
(C) (CH₃)₃N → tertiary amine
(D) NH₃ → least basic

Increasing order of basicity (least → most):

$\text{NH₃} < \text{(CH₃)₃N} < \text{CH₃NH₂} < \text{(CH₃)₂NH}$

✔ Correct order: (D), (C), (B), (A)