Which among the following salts turns red litmus blue in its aqueous solution?

Calculate dissociation constant of a weak monobasic acid if it is $0.05 \%$ dissociated in 0.02 M solution.

A buffer solution contains equal concentrations of weak acid and its salt with strong base. Calculate pH of buffer solution if dissociation constant of weak acid is $1.8 \times 10^{-5}$.

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