Which of the following mixtures in water acts as a basic buffer?

Assertion : In a titration of weak acid and $NaOH$,the $pH$ at half equivalence point is $pK_a$.
Reason : At half equivalence point,it forms an acidic buffer and the buffer capacity is maximum where $[acid] = [salt]$.

$A$ sample of $100 \ mL$ of $0.10 \ M$ acid $HA$ $(K_a = 1 \times 10^{-5})$ is titrated with standard $0.2 \ M \ KOH$. How many $mL$ of $KOH$ will have to be added when the $pH$ in the titration flask will be $5.00$?

$20 \ mL$ of $0.1 \ (N)$ acetic acid is mixed with $10 \ mL$ of $0.1 \ (N)$ solution of $NaOH$. The $pH$ of the resulting solution is ($pK_a$ of acetic acid is $4.74$). (in $.74$)

$A$ student needs to prepare a buffer solution of propanoic acid and its sodium salt with $pH$ $4$. The ratio of $\frac{[CH_{3}CH_{2}COO^{-}]}{[CH_{3}CH_{2}COOH]}$ required to make the buffer is .....
Given: $K_{a}(CH_{3}CH_{2}COOH) = 1.3 \times 10^{-5}$

$A$ buffer solution is prepared by mixing $0.2 \ M$ sodium acetate and $0.1 \ M$ acetic acid. If $pK_{a}$ for acetic acid is $4.7$,find the $pH$.