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

$A$ solution of $0.1 \ mol$ of $CH_3NH_2$ $(K_b = 5 \times 10^{-4})$ and $0.08 \ mol$ of $HCl$ is diluted to $1 \ L$. The $pOH$ of the resulting solution is $(\log 1.25 = 0.1)$.

$A$ $0.15 \text{ mol}$ of pyridinium chloride is added to $500 \text{ cm}^3$ of $0.2 \text{ M}$ pyridine solution. Assuming no change in volume upon mixing, what is the $pH$ of the resulting solution? (Given: $pK_b$ of pyridine $= 8.75$)

When $NaOH$ is added to a $CH_3COOH$ solution,$60\%$ of the acid is neutralized. If the $pK_a$ is $4.7$,the $pH$ of the resulting solution is:

$pH$ of a mixture of $1 \ M \ HA$ $(pK_a = 4.2)$ and $1 \ M \ NaA$ is $4.5$. In $300 \ mL$ of buffer,the volume of $HA$ is $....... \ mL$ $[\log \ 2 = 0.3]$

Which of the following mixtures in water acts as a basic buffer?