Three reactions involving $$H_2PO_4^−$$ are given below :

(i) H₃PO₄ + H₂O $$\to$$ H₃O⁺ + $$H_2PO_4^−$$

(ii) $$H_2PO_4^−$$ + H₂O $$\to$$ $$HPO_4^{2−}$$ + H₃O⁺

(iii) $$H_2PO_4^−$$ + OH^- $$\to$$H₃PO₄ + O^2-

In which of the above does $$H_2PO_4^−$$ act as an acid?

Solubility product of silver bromide is 5.0 $$\times$$ 10^–13. The quantity of potassium bromide (molar mass taken as 120g of mol^–1) to be added to 1 litre of 0.05 M solution of silver nitrate to start the precipitation of AgBr is :

At 25°C, the solubility product of Mg(OH)₂ is 1.0 $$\times$$ 10^–11. At which pH, will Mg²⁺ ions start precipitating in the form of Mg(OH)₂ from a solution of 0.001 M Mg²⁺ ions?

Solid Ba(NO₃)₂ is gradually dissolved in a 1.0 $$\times$$ 10^-4 M Na₂CO₃ solution. At what concentration of Ba²⁺ will a precipitate begin to form ?
(K_sp for BaCO₃ = 5.1 $$\times$$ 10⁻⁹ )