The correct sequence regarding base strength of aliphatic amines in aqueous solution is

The correct sequence regarding base strength of aliphatic amines in aqueous solution is ${\mathrm{R}}_2\mathrm{NH}>{\mathrm{RNH}}_2>{\mathrm{R}}_3\mathrm{N}$.

The base strength of aliphatic amines is decided by the following two factors. Induction factor Increasing replacement of H by R (electron-releasing group) increases electron density on N, thus making it more basic.

Solvation factor Stabilization of conjugate acid through H-bonding with water. More the number of H atoms, more the stability and thus more basic the amine. Thus, induction and solvation operate in opposite directions. Induction dominates to make all three alkylamines more basic than ammonia. However, adding a third R as in ${\mathrm{R}}_3\mathrm{N}$ does not further enhance the basicity because now the opposing solvation effect assumes more importance.

Hence, option B is correct.