Which one of the following pairs of solution is not an acidic buffer ?

The K_sp of Ag₂CrO₄,  AgCl,  AgBr  and Agl  are respectively, 1.1 $$ \times $$ 10^$$-$$12, 1.8 $$ \times $$ 10^$$-$$10, 5.0 $$ \times $$ 10^$$-$$13, 8.3 $$ \times $$ 10^$$-$$17. Which one of the following salts will precipitate last if AgNO₃ solution is added to the solution containing equal moles of NaCl, NaBr, Nal and Na₂CrO₄?

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