Which of the following mixtures of solutions can function as a buffer solution?

Which of the following solutions can act as a buffer?

$3 \; g$ of acetic acid is added to $250 \; mL$ of $0.1 \; M \; HCl$ and the solution is made up to $500 \; mL$. To $20 \; mL$ of this solution,$\frac{1}{2} \; mL$ of $5 \; M \; NaOH$ is added. The $pH$ of the solution is: [Given: $pK_{a}$ of acetic acid $= 4.75$,molar mass of acetic acid $= 60 \; g/mol$,$\log 3 = 0.4771$]. Neglect any changes in volume.

The $pH$ of a solution at $25\,^oC$ containing $0.10\,M$ sodium acetate and $0.03\,M$ acetic acid is ($pK_a$ for $CH_3COOH = 4.57$)

$20 \ mL$ solution contains $0.1 \ M \ NH_4Cl$ and $0.01 \ M \ NH_4OH$. By adding which one will its $pH$ not change?

Aqueous solutions of $HNO_{3}$,$KOH$,$CH_{3}COOH$,and $CH_{3}COONa$ of identical concentration are provided. The pair$(s)$ of solutions which form a buffer upon mixing is (are):