Which of the following is a buffer solution?

Which of the following buffer solutions will have the highest acidic character?

$2 \ g$ acetic acid and $3 \ g$ sodium acetate are present in $100 \ mL$ aqueous solution. What will be the $pH$ of the solution if the ionisation constant of acetic acid is $1.8 \times 10^{-5}$?

Which of the following is a buffer solution?

When $30 \ mL$ of $0.2 \ M \ NH_4OH$ is added to $30 \ mL$ of $2 \ M \ NH_4Cl$ solution. If the $pH$ of the buffer formed is $8.2$,what is the $pK_b$ of $NH_4OH$?

The dissociation constant of $HCN$ is $5 \times 10^{-10}$. The $pH$ of the solution prepared by mixing $1.5 \, mole$ of $HCN$ and $0.15 \, mole$ of $KCN$ in water and making up the total volume to $0.5 \, dm^3$ is (in $.302$)