How many coulombs are required to oxidise 0.1 mole of $\mathrm{H}_2 \mathrm{O}$ to oxygen?

A current of 3 A is passed through a molten calcium salt for 1 hr 47 min 13 s . The mass of calcium deposited is (Molar mass of $\mathrm{Ca}=40 \mathrm{~g} \mathrm{~mol}^{-1}$ )

The value of ' $A$ ' in the equation $\lambda_{\mathrm{m}}=\lambda_{\mathrm{m}}^{\circ}-A \sqrt{C}$ is same for the pair

The resistance of $$0.1 \mathrm{~M}$$ weak acid $$\mathrm{H} A$$ in a conductivity cell is $$2 \times 10^3 \mathrm{~Ohm}$$. The cell constant of the cell is $$0.78 ~\mathrm{C} \mathrm{~m}^{-1}$$ and $$\lambda_{\mathrm{m}}^{\circ}$$ of acid $$\mathrm{H} A$$ is $$390 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$$. The $$\mathrm{pH}$$ of the solution is