Which of the following is a buffer solution of strong acidic nature?

Give the importance of buffer solution.

The $K_a$ of $CH_3COOH$ is $1.8 \times 10^{-5}$. How many grams of $CH_3COONa$ are required in $0.1 \ M \ CH_3COOH$ to form a solution having $pH = 4.0$? (Molecular mass of $CH_3COONa = 82 \ g \ mol^{-1}$)

$A$ 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 $5.00$?

When an acid or alkali is mixed with a buffer solution,the $pH$ of the buffer solution:

$A$ certain buffer solution contains equal concentrations of $X^{-}$ and $HX$. The $K_a$ for $HX$ is $10^{-8}$. The $pH$ of the buffer is