The treatment of phenol with phthalic anhydride in the presence of concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$ produces

The treatment of phenol with phthalic anhydride in the presence of concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$ produces phenolphthalein

One molecule of phthalic anhydride combines with two molecules of phenol to create a molecule of phenolphthalein in the presence of concentrated sulfuric acid. The process results in the loss of one water molecule. This is a condensation reaction as a result.

Hence option D is correct