Which will make basic buffer?

Following solutions were prepared by mixing different volumes of NaOH and HCl of different concentrations :

A. 60 mL $${M \over {10}}$$ HCl + 40 mL $${M \over {10}}$$ NaOH

B. 55 mL $${M \over {10}}$$ HCl + 45 mL $${M \over {10}}$$ NaOH

C. 75 mL $${M \over {5}}$$ HCl + 25 mL $${M \over {5}}$$ NaOH

D. 100 mL $${M \over {10}}$$ HCl + 100 mL $${M \over {10}}$$ NaOH

pH of which one of them will be equal to 1?

The solubility of BaSO₄ in water is 2.42 × 10^–3 g L^–1 at 298 K. The value of its solubility product (K_sp) will be (Given molar mass of BaSO₄ = 233 g mol^–1)

Concentration of the Ag⁺ ions in a saturated solution of Ag₂C₂O₄ is 2.2 $$ \times $$ 10^$$-$$4 mol L^$$-$$1. Solubility product of Ag₂C₂O₄ is