Observe the following reactions, $\mathrm{A}+{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{SO}}_2\mathrm{Cl} \stackrel{-\mathrm{OH}}{⟶}\stackrel{\mathrm{KOH}}{⟶}$ Clear solution $\stackrel{{\mathrm{H}}^{+}}{\to }$ Substance is soluble in acidic medium

$\mathrm{B}+{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{SO}}_2\mathrm{Cl}\stackrel{-\mathrm{OH}}{⟶}$ Insoluble substance in ${\mathrm{H}}^{+}/{\mathrm{OH}}^{-}$

$\mathrm{C}+{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{SO}}_2\mathrm{Cl}\stackrel{-\mathrm{OH}}{⟶}$ Insoluble in base but soluble in ${\mathrm{H}}^{+}\stackrel{{\mathrm{H}}^{+}}{⟶}$ Clear solution.

A, B and C are respectively

1^o amine forms N-alkyl benzene sulphonamide with ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{SO}}_2\mathrm{Cl}$ which is soluble in alkali.
2^o amine forms N, N-dialkyl benzene sulphonamide, which is insoluble in alkali as well as acid.
3^o amines do not react with ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{SO}}_2\mathrm{Cl}$ and hence are soluble in acid. Thus, A, B, and C here represent 1^o, 2^o and 3^o amines respectively.