Which salt will give a basic solution on hydrolysis?

$pK_a$ of acetic acid is $4.74$. The concentration of $CH_3COONa$ is $0.01 \ M$. The $pH$ of $CH_3COONa$ is

Which one of the following substances will be a mixed salt?

The $pK_a$ of a weak acid,$HA,$ is $4.80.$ The $pK_b$ of a weak base,$BOH,$ is $4.78.$ The $pH$ of an aqueous solution of the corresponding salt,$BA,$ will be

Why is the following anionic hydrolysis correct?
$X^{-} + H_2O \rightleftharpoons HX + OH^{-}$

The $pH$ of an aqueous solution of $MgCl_2$ is .......