Identify the product formed from chlorobenzene on heating with conc. $\mathrm{HNO}_3$ in presence of conc. $\mathrm{H}_2 \mathrm{SO}_4$.

Nitration of chlorobenzene with concentrated $\mathrm{HNO}_3$ and concentrated $\mathrm{H}_2\mathrm{SO}_4$ proceeds via electrophilic aromatic substitution, where the nitronium ion $\mathrm{NO}_2^+$ acts as the electrophile.

The chlorine substituent exhibits both an electron-withdrawing inductive effect and an electron-donating resonance effect, making it overall deactivating but ortho–para directing. Consequently, substitution occurs at the ortho and para positions, yielding a mixture of 1-chloro-2-nitrobenzene and 1-chloro-4-nitrobenzene.

Option A is incorrect as it ignores the ortho product, option B is incorrect as it ignores the para product, and option D is incorrect since trinitration requires harsher conditions.