Which of the following is a mixed salt?

The aqueous solution of $FeCl_3$ is acidic due to

Arrange the aqueous solutions of the following salts in the increasing order of $pH$: $CuSO_4$ $(I)$,$NaCN$ $(II)$,$KCl$ $(III)$.

The concentration of $[H^{+}]$ in a $0.1 \, M \, CH_3COONa$ solution [$K_a = 10^{-5}$] is equal to ......

$20\,mL$ of $0.1\,M\,NH_{4}OH$ is mixed with $40\,mL$ of $0.05\,M\,HCl$. The $pH$ of the mixture is nearest to. (Given: $K_{b}(NH_{4}OH) = 1 \times 10^{-5}, \log 2 = 0.30, \log 3 = 0.48, \log 5 = 0.69, \log 7 = 0.84, \log 11 = 1.04$) (in $.2$)

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