Which has the highest $pH$?

$pH=\log .\frac{1}{\left[H^{+}\right]}$
pH is inversely proportional to hydrogen ion concentration. As concentration of $H^{+}$ decreases pH increases and vice-versa.
Ammonium chloride $\left(N{H}_{4}Cl\right)$ is a salt of weak base and strong acid. So, its aqueous solution will be acidic as
$N{H}_{4}Cl+H_{2}O\to \underset{\text{Weak base}}{N{H}_{4}OH}+\underset{\text{Strong acid}}{HN{O}_3}$
So, pH of $NaN{O}_3$ is 7.
Potassium acetae $\left(C{H}_{3}COOK\right)$ is salt of strong base and weak acid. Its aqueous solution will be basic and pH value will be greater than 7.
Sodium nitrate $\left(NaN{O}_3\right)$ is the salt of strong acid and strong and strong base. So, its aqueous solution is neutral as
$NaN{O}_3+H_{2}O\to \underset{\text{Strong base}}{\mathrm{NaOH}}+\underset{\text{Strong acid}}{HN{O}_3}$
So, pH of $NaN{O}_3$ is 7.
Potassium acetate $\left(C{H}_{3}COOK\right)$ is salt of strong base and weak acid. Its aqueous solution will be basic and pH value will be greater than $7\approx 8.8$
$C{H}_{3}CO{O}^{-}{K}^{+}+H_{2}O\to \underset{\text{Weak acid}}{C{H}_{3}COOH}+\underset{\text{Strong base}}{\mathrm{KOH}}$
Sodium carbonate $\left(N{a}_{2}C{O}_3\right)$ is a salt of strong base and weak acid. Its aqueous solution is also basic and its pH value will be more than 10.
i.e. highest among them.
$N{a}_{2}C{O}_3+H_{2}O\to \underset{\text{Strong base}}{2NaOH}+\underset{\text{Weak acid}}{H_{2}C{O}_3}$