Concept of basicity

Basicity depends on the availability of the lone pair on nitrogen for donation.

• In $NH_3$, nitrogen has a lone pair.
• In alkyl amines, alkyl groups like $CH_3$ show the $+I$ effect (electron-donating inductive effect), which increases electron density on nitrogen.
• Hence, alkyl amines are generally more basic than ammonia.

Compare the given bases

The compounds are:

• $NH_3$ (ammonia)
• $CH_3NH_2$ (methylamine, a primary amine)
• $(CH_3)_2NH$ (dimethylamine, a secondary amine)

Effect of alkyl groups

As the number of methyl groups attached to nitrogen increases, the electron density on nitrogen increases due to the $+I$ effect.

Therefore: $NH_3 < CH_3NH_2 < (CH_3)_2NH$

Check options

• A: $(CH_3)_2NH < NH_3 < CH_3NH_2$ ❌ wrong
• B: $NH_3 < CH_3NH_2 < (CH_3)_2NH$ ✅ correct
• C: $CH_3NH_2 < (CH_3)_2NH < NH_3$ ❌ wrong
• D: $CH_3NH_2 < NH_3 < (CH_3)_2NH$ ❌ wrong

Final answer

The correct order of increasing basic nature is: $NH_3 < CH_3NH_2 < (CH_3)_2NH$