JEE Advanced 2020 · Paper 1, Chemistry question 8

(A) The triphenylmethyl anion spreads its charge over three rings, which is why $\ce{Ph3CH}$ is acidic. True.

(B) Cyclopentadienyl anion: a planar ring with 6 π electrons, so it is aromatic. True.

(C) $\ce{NO2}$ withdraws electrons and stabilises the aryl anion, so nitrobenzene's ring C-H is more acidic than benzene's. True.

(D) The approximate pKa values are:

• cyclopentadiene (IV) about 16;
• ethyne (V) about 25;
• triphenylmethane (I) about 31.5;
• benzene (II) about 43;
• methane (III) about 48.

So the order is IV > V > I > II > III, not I > IV > V > II > III. False.

(A), (B), (C)