Which buffer solution out of the following will have $pH > 7$?

What is $[H^{+}]$ of a solution that is $0.01 \ M$ in $HCN$ and $0.02 \ M$ in $NaCN$ ($K_a$ for $HCN = 6.2 \times 10^{-10}$)?

Aqueous solutions of $HNO_3$,$KOH$,$CH_3COOH$,and $CH_3COONa$ of identical concentrations are provided.
The pair$(s)$ of solutions which form a buffer upon mixing is(are):
$A$. $HNO_3$ and $CH_3COOH$
$B$. $KOH$ and $CH_3COONa$
$C$. $HNO_3$ and $CH_3COONa$
$D$. $CH_3COOH$ and $CH_3COONa$

What volume (in $mL$) of $0.10 \, M$ sodium formate is required to be added to $50 \, mL$ of $0.05 \, M$ formic acid to prepare a buffer solution with $pH = 4.0$? (Given: $pK_a$ of formic acid $= 3.7$)

All the given solutions have the same concentration. Mixing equal volumes of which of the following will produce a buffer solution?
$A = NH_4Cl$; $B = CH_3COONa$; $C = NH_4OH$; $D = CH_3COOH$

Calculate the $pH$ of a buffer solution containing $0.1 \text{ M } CH_3COOH$ and $0.1 \text{ M } CH_3COONa$ $[K_a = 1.8 \times 10^{-5}]$.