JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Compounds Containing Nitrogen

The strongest conjugate acid is produced from the weakest base, because a weak base binds the added proton most loosely and so gives the most readily ionised cation. The four bases are substituted anilines, whose strength depends on the electron density left on nitrogen. The electron-releasing $-\mathrm{OC}{\mathrm{H}}_3$ and $-\mathrm{C}{\mathrm{H}}_3$ groups raise the basicity of $p$-anisidine and $p$-toluidine, and unsubstituted aniline is intermediate. In $p$-nitroaniline the $-\mathrm{N}{\mathrm{O}}_2$ group withdraws electron density strongly by resonance and induction, leaving the nitrogen lone pair least available, so it is the weakest base. The strongest conjugate acid results from $p$-nitroaniline.