Identify correct decreasing order of basic strength of amines from following.

Amine basicity in aqueous solution is governed by three competing factors: inductive effects, solvation, and steric hindrance.

Alkyl groups donate electrons through the +I effect, increasing electron density on nitrogen and enhancing basicity. This would suggest the order: tertiary > secondary > primary amine.

However, aqueous solvation stabilizes the conjugate acid through hydrogen bonding. Primary amines form three H-bonds ($\mathrm{CH}_3\mathrm{NH}_3^+$), secondary amines two ($(\mathrm{CH}_3)_2\mathrm{NH}_2^+$), and tertiary amines only one ($(\mathrm{CH}_3)_3\mathrm{NH}^+$). Solvation alone would produce the order: primary > secondary > tertiary.

Tertiary amines additionally experience steric hindrance from bulky groups, further reducing basicity.

The observed order results from balancing these effects: secondary amines optimize inductive gain and solvation, while tertiary amines suffer from poor solvation and steric effects. The experimental order is:

$(\mathrm{CH}_3)_2\mathrm{NH} > \mathrm{CH}_3\mathrm{NH}_2 > (\mathrm{CH}_3)_3\mathrm{N}$

Option B matches this sequence.

The correct choice is $\boxed{\text{B}}$