Which of the following will not function as a buffer solution?

Calculate the $pH$ of a $2 \, L$ solution containing $0.1 \, M \, CH_3COOH$ and $0.1 \, M \, (CH_3COO)_2Ba$. Given $K_a (CH_3COOH) = 1.8 \times 10^{-5}$.

The $pH$ of blood is maintained by a proper balance of $H_2CO_3$ and $NaHCO_3$ concentrations. What volume of $5 \, M \, NaHCO_3$ solution should be mixed with $10 \, mL$ of $2 \, M \, H_2CO_3$ to maintain a $pH$ of $7.4$ (in $, mL$)? (Given: $K_a$ for $H_2CO_3 = 7.8 \times 10^{-7}$)

Calculate $pH$ of the solution obtained by mixing $50 \ mL$ of $0.2 \ M$ $NH_4Cl$ solution and $75 \ mL$ of $0.1 \ M$ $NaOH$ solution. Given $pK_b$ for aqueous $NH_3$ is $4.74$.

Which buffer is present in human blood :-

$A$ buffer solution can be prepared from a mixture of