The compound shown is heated with aqueous $\mathrm{NaOH}$ at about 433 K and the mixture is then acidified. Which structure is the main organic product?

A single para nitro group activates the ring towards nucleophilic aromatic substitution, but only under forcing conditions (about 433 K). Hydroxide replaces chlorine, giving 4-nitrophenol after acidification. The meta-nitrophenol would need rearrangement, 4-nitroaniline needs ammonia, and 4-chlorophenol would require loss of the nitro group.