$A$ buffer solution has equal volumes of $0.2 \ M \ NH_4OH$ and $0.02 \ M \ NH_4Cl$. The $pK_b$ of the base is $5$. The $pH$ is

Observe the following four solutions :
$P : 10 \ mL, 0.1 \ M \ NaOH + 5 \ mL, 0.1 \ M \ HCl$
$Q : 10 \ mL, 0.1 \ M \ NaOH + 15 \ mL, 0.1 \ M \ CH_3COOH$
$R : 10 \ mL, 0.1 \ M \ NH_3 + 10 \ mL, 0.1 \ M \ NH_4Cl$
$S : 10 \ mL, 0.05 \ M \ NaF + 5 \ mL, 0.1 \ M \ HF$
Which of above solutions act as buffer?

The $pH$ of a buffer solution containing $0.2 \ mol/L$ $CH_3COONa$ and $1.5 \ mol/L$ $CH_3COOH$ is ($K_a$ for acetic acid is $1.8 \times 10^{-5}$).

The ratio of volumes of $CH_3COOH$ $0.1 \ N$ to $CH_3COONa$ $0.1 \ N$ required to prepare a buffer solution of $pH$ $5.74$ is (Given,$pK_a$ of $CH_3COOH$ is $4.74$)

Which of the following is not a buffer solution?

What would be the $pH$ of a solution obtained by mixing $5 \ g$ of acetic acid and $7.5 \ g$ of sodium acetate and making the volume equal to $500 \ mL$? $(K_a = 1.75 \times 10^{-5}, pK_a = 4.76)$