An aqueous solution of which of the following salts will have a pH...

A solution with $\mathrm{pH} > 7$ is basic, which is formed by the hydrolysis of a salt derived from a weak acid and a strong base.

$\mathrm{NH_4Cl}$ is a salt of a strong acid ($\mathrm{HCl}$) and a weak base ($\mathrm{NH_4OH}$). Its aqueous solution is acidic, so $\mathrm{pH} < 7$.

$\mathrm{KNO_3}$ is a salt of a strong acid ($\mathrm{HNO_3}$) and a strong base ($\mathrm{KOH}$). Its aqueous solution is neutral, so $\mathrm{pH} = 7$.

$\mathrm{CH_3COOK}$ is a salt of a weak acid ($\mathrm{CH_3COOH}$) and a strong base ($\mathrm{KOH}$). The acetate ion undergoes anionic hydrolysis to produce $\mathrm{OH^-}$ ions, making the solution basic, so $\mathrm{pH} > 7$.

$\mathrm{Na_2SO_4}$ is a salt of a strong acid ($\mathrm{H_2SO_4}$) and a strong base ($\mathrm{NaOH}$). Its aqueous solution is neutral, so $\mathrm{pH} = 7$.

Answer: $\mathrm{CH_3COOK}$