Basicity Of Amines

Basicity of an amine depends on the availability of the lone pair on nitrogen, which is governed by the inductive electron-donating effect of alkyl groups and, in solution, by solvation of the conjugate acid. In the gas phase there is no solvent, so only the inductive effect operates: each additional methyl group pushes electron density toward nitrogen and increases the stability of the protonated cation. Consequently the order is purely additive and follows (CH3)3N > (CH3)2NH > CH3NH2. The option CH3NH2 > (CH3)2NH > (CH3)3N reflects the reverse, which is incorrect because it ignores the cumulative +I effect. The two options placing dimethylamine first describe the aqueous-phase anomaly, where steric hindrance and reduced hydration of the bulky trimethylammonium ion lower trimethylamine's basicity, but the question specifies the gas phase. This anomaly between gas and solution phases is a standard JEE discrimination point rooted in the NCERT discussion of solvation versus inductive effects, where the three competing factors are inductive donation, steric hindrance, and hydration of the cation. As a plausibility check, the trend cleanly increases with methyl substitution, exactly as expected when solvation is removed from consideration and only electron donation matters.