When $500 \, mL$ of $0.2 \, M$ acetic acid is added to $500 \, mL$ of $0.30 \, M$ sodium acetate solution,what is the $pH$ of the resulting solution? (Given: Dissociation constant of acetic acid $K_a = 1.5 \times 10^{-5}$)

The $OH^{-}$ concentration in a mixture of $5.0 \ mL$ of $0.0504 \ M \ NH_{4}Cl$ and $2 \ mL$ of $0.0210 \ M \ NH_{3}$ solution is $x \times 10^{-6} \ M$. The value of $x$ is ..... .
(Nearest integer)
$[ \text{Given } K_{w}=1 \times 10^{-14} \text{ and } K_{b}=1.8 \times 10^{-5} ]$

The $pH$ of blood is maintained by a proper balance of $H_2CO_3$ and $NaHCO_3$ concentrations. What volume of $5 \, M \, NaHCO_3$ solution should be mixed with $10 \, mL$ of $2 \, M \, H_2CO_3$ to maintain a $pH$ of $7.4$ (in $, mL$)? (Given: $K_a$ for $H_2CO_3 = 7.8 \times 10^{-7}$)

Which of the following is not a buffer solution?

Calculate the $pH$ of a buffer solution prepared by mixing $30 \ mL$ of $0.1 \ M$ $NaOH$ and $100 \ mL$ of $0.1 \ M$ $CH_3COOH$. (Given: $pK_a$ of $CH_3COOH = 4.76$)

Which of the following solutions can act as a buffer?