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

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 ?

At 100^oC the K_w of water is 55 times its value at 25^oC. What will be the pH of neutral solution? (log 55 = 1.74)