Which of the following is not a buffer solution?

Given below are two statements:
Statement $I$: $A$ buffer solution is the mixture of a salt and an acid or a base mixed in any particular quantities.
Statement $II$: Blood is a naturally occurring buffer solution whose $pH$ is maintained by $H_2CO_3 / HCO_3^{-}$ concentrations.
In the light of the above statements,choose the correct answer from the options given below.

At $25 \, ^\circ C$,the $K_a$ for $HCN$ is $5 \times 10^{-10}$. What volume (in $mL$) of $5 \, M \, KCN$ solution must be added to $10 \, mL$ of $2 \, M \, HCN$ solution to maintain a constant $pH$ of $9$?

Calculate the $pH$ of a buffer solution prepared by mixing $30 \ mL$ of $0.1 \ M$ $NaOH$ and $100 \ mL$ of $0.1 \ M$ $CH_3COOH$. (Given: $pK_a$ of $CH_3COOH = 4.76$)

$A$ 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? $(pK_a = 4.74)$

Which buffer solution out of the following will have $pH > 7$?