Which of the following solutions cannot act as a buffer?

$20 \ mL$ of $0.1 \ M$ acetic acid is mixed with $50 \ mL$ of potassium acetate. $K_a$ of acetic acid $= 1.8 \times 10^{-5}$ at $27^{\circ} C$. Calculate the concentration of potassium acetate if the $pH$ of the mixture is $4.8$. (in $M$)

Which of the following will form a basic buffer solution?

$A$ solution which is resistant to change of $pH$ upon the addition of an acid or a base is known as

$A$ certain buffer solution contains equal concentrations of $3.9 \times 10^{-5} \ M$ $X^{-}$ and $HX$. The $K_b$ for $X^{-}$ is $10^{-10}$. The $pH$ of the buffer is: