Which of the following salts will give highest $pH$ in water?

The correct option is D $N{a}_{2}C{O}_3$
$NaCl$ and $KCl$ are the salts of a strong acid and strong base. They do not undergo hydrolysis. Their aqueous solutions are neutral.

$N{a}_{2}C{O}_3$ is basic due to hydrolysis of $C{O}_3^{2-}$ ion

$C{O}_3^{2-}+H_{2}O\rightleftharpoons HC{O}_3^{-}+O{H}^{-}$

Hence, $N{a}_{2}C{O}_3$ will give highest pH in water.