Which from the following equations represents the relation between solubility ( $\mathrm{mol} \mathrm{~L}^{-1}$ ) and solubility product for a salt $\mathrm{B}_3 \mathrm{A}_2$ ?

Calculate solubility $\left(\mathrm{moldm}^{-3}\right)$ of a sparingly soluble electrolyte AB at 298 K if its solubility product is $1.6 \times 10^{-5}$ ?

What is the pH of $10^{-8} \mathrm{M~HCl}$ solution?

Which from following buffers is used to maintain the pH of human blood naturally?