Amongst the following solutions,the buffer solution is

If the molar concentrations of a base and its conjugate acid are the same, then the $pOH$ of the buffer solution is:

The $pH$ of a sodium acetate buffer solution is given by the Henderson-Hasselbalch equation: $pH = pK_a + \log \frac{[Salt]}{[Acid]}$. For acetic acid,if $[Salt] = [Acid] = 0.1 \ M$,then the $pH$ of the solution is: $[K_a = 1.8 \times 10^{-5}]$

Which one of the following pairs of solutions is not an acidic buffer?

Which of the following cannot act as a buffer solution?

$100 \ mL$ of $0.1 \ M$ $HA$ (weak acid) and $100 \ mL$ of $0.2 \ M$ $NaA$ are mixed. What is the $pH$ of the resultant solution? ($K_{a}$ of $HA$ is $10^{-5}$; $\log 2 = 0.3$)