Which has highest pH : -

$NH_4Cl$ is a salt of a weak base and a strong acid; its solution is acidic (pH $\lt$ 7).
$NaNO_3$ is a salt of a strong acid and a strong base; its solution is neutral (pH = 7).
$CH_3COOK$ and $Na_2CO_3$ are salts of weak acids with strong bases; both give basic solutions by hydrolysis.
Carbonic acid is a much weaker acid ($K_{a2} \approx 4.7 \times 10^{-11}$) than acetic acid ($K_a \approx 1.8 \times 10^{-5}$), so the carbonate ion is a much stronger base than acetate: $CO_3^{2-} + H_2O \rightleftharpoons HCO_3^- + OH^-$ gives more $OH^-$.
So $Na_2CO_3$ has the highest pH.