The constant acidity and basicity of a buffer solution is due to........

The dissociation constant of acetic acid is $x \times 10^{-5}$. When $25 \ mL$ of $0.2 \ M \ CH_3COONa$ solution is mixed with $25 \ mL$ of $0.02 \ M \ CH_3COOH$ solution,the $pH$ of the resultant solution is found to be equal to $5$. The value of $x$ is $..........$.

$50 \ mL$ of $0.02 \ M$ $NaHSO_4$ is mixed with $50 \ mL$ of $0.02 \ M$ $Na_2SO_4$. Calculate the $pH$ of the resulting solution. $[pK_{a2} (H_2SO_4) = 2]$

Which of the following mixtures will have the lowest $pH$ at $298 \ K$?

For preparing a buffer solution of $pH = 5$ by mixing sodium acetate and acetic acid,the ratio of the concentration of salt and acid should be $(K_a = 10^{-5})$:-

$A$ solution contains $0.2 \ M \ NH_4OH$ and $0.2 \ M \ NH_4Cl$. If $1.0 \ mL$ of $0.001 \ M \ HCl$ is added,what will be the $[OH^-]$ of the resulting solution? [Given: $K_b = 2 \times 10^{-5}$]