Chemistry - GOC Question with Solution | TestHub

${\mathrm{pK}}_{\mathrm{a}}=-{\mathrm{logK}}_{\mathrm{a}}$, here ${\mathrm{K}}_{\mathrm{a}}$ acid dissociation constant. More the ${\mathrm{K}}_{\mathrm{a}}$ value, stronger is the acidic nature of the respective acid.

Hence, the lower ${\mathrm{pK}}_{\mathrm{a}}$ value denotes a more powerful acid.  Phenols are more acidic than alcohols. Hence, ethanol has more ${\mathrm{pK}}_{\mathrm{a}}$ value. Nitro group is the electron withdrawing group, hence it increases the acidic nature of phenols.  Among the given phenols para nitrophenol  is stronger acid. The ${\mathrm{pK}}_{\mathrm{a}}$ values are matched below.

Ethanol $\to$$15.9$

Phenol$\to 10$

$\mathrm{m}-$Nitrophenol $\to 8.3$

$\mathrm{p}-$Nitrophenol$\to 7.1$

Hence, the answer is option D.