Which one of the following pairs of solutions is not an acidic buffer?

$A$ solution contains $0.1 \ mol$ of acetic acid and $0.1 \ mol$ of sodium acetate in $500 \ mL$ of solution. If the $pH$ of the solution is $4.74$,find the ionization constant $(K_a)$ of acetic acid.

$A$ buffer solution contains $100 \ mL$ of $0.01 \ M \ CH_3COOH$ and $200 \ mL$ of $0.02 \ M \ CH_3COONa$. If $700 \ mL$ of $1 \ M \ NaCl$ is added,what are the $pH$ values before and after the addition? $(pK_a = 4.74)$

The $pH$ of blood does not appreciably change by a small addition of acid or a base because blood

$A$ buffer solution is prepared with a concentration of $0.30 \ M \ NH_3$ and $0.20 \ M \ NH_4^+$. If the equilibrium constant for $NH_3$ is $K_b = 1.8 \times 10^{-5}$,what will be the $pH$ of this solution?

The $pH$ of blood is