Which of the following salts will give highest pH in water?

Accumulation of lactic acid (HC₃H₅O₃), a monobasic acid in tissues leads to pain and a feeling of fatigue. In a 0.10 M aqueous solution, lactic acid is 3.7% dissociates. The value of dissociation constant, K_a, for this acid will be

The dissociation constant of weak acid is 1 $$ \times $$ 10^$$-$$4. In order to prepare a buffer solution with a pH = 5, the [Salt]/[Acid] ratio should be

The values of K_sp of CaCO₃ and CaC₂O₄ are 4.7 $$ \times $$ 10^$$-$$9 and 1.3 $$ \times $$ $$-$$9 respectively at 25^oC. If the mixture of these two is washed with water, what is the concentration of Ca²⁺ ions in water ?