Which of the following is a buffer solution of strong acidic nature?

The $pH$ of a buffer solution made by mixing $25 \ mL$ of $0.02 \ M$ $NH_4OH$ and $25 \ mL$ of $0.2 \ M$ $NH_4Cl$ at $25^{\circ}C$ is ($pK_b$ of $NH_4OH = 4.8$).

What is the $pH$ of a buffer solution formed by mixing $0.01 \ M$ acetic acid and $0.05 \ M$ sodium acetate $(pK_a = 4.7447)$?

Buffer solution is prepared by mixing

Find the $pH$ of a solution formed by mixing equal volumes of $0.1 \text{ M}$ sodium propionate and $0.1 \text{ M}$ propionic acid. (Given: The dissociation constant of propionic acid is $K_a = 1.3 \times 10^{-5}$)

In order to prepare a buffer solution of $pH = 5.74$,sodium acetate is added to acetic acid. If the concentration of acetic acid in the buffer is $1.0 \ M$,the concentration of sodium acetate in the buffer is $......... \ M$. (Round off to the nearest integer).
[Given: $pKa$ (acetic acid) $= 4.74$]