Which of the following pairs constitutes a buffer?

The buffer system which helps to maintain the $pH$ of blood between $7.26$ to $7.42$ is:

Which among the following pairs is not an acidic 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 $[acid] = [salt]$.

Find the $pH$ of a buffer solution prepared by mixing $300 \, mL$ of $0.3 \, M \, NH_3$ and $500 \, mL$ of $0.5 \, M \, NH_4Cl$. Given $K_b$ for $NH_3 = 1.8 \times 10^{-5}$.

$A$ buffer solution is formed by a weak acid and its salt with a strong base,or a weak base and its salt with a strong acid. In which of the following pairs is this characteristic found?