How many $mL$ of $0.2 \, M \, KCN$ should be mixed with $200 \, mL$ of $0.1 \, M \, HCN$ so as to make a mixture of $pH = 3$ ($pK_a$ for $HCN = 6$)?

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.

$A$ buffer solution of $pH = 9.80$ is to be prepared from $1 \ M \ NH_4Cl$ and $1 \ M \ NH_3$ solution. $pK_{b}$ of $NH_3$ is $4.74$. In $1 \ L$ of the buffer solution,the volume of $NH_4Cl$ solution required is $(\log 0.28 = -0.54) :-$ (in $mL$)

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

What are buffer solutions? Explain types of buffer solutions with examples.

Which of the following mixtures is called an acidic buffer?