Complete and balance the following equation:

Zn + $$NO_3^- \to$$ Zn²⁺ + $$NH_4^+$$

Complete and balance the following equation:

$$Cr_2O_7^{2-}$$ + C₂H₄O $$\to$$ C₂H₄O₂ + Cr³⁺

The density of a 3 M Sodium thiosulphate solution (Na₂S₂O₃) is 1.25 g per ml. Calculate

(i) the percentage by weight of sodium thiosulphate,

(ii) the mole fraction of sodium thiosulphate and

(iii) the molalities of Na⁺ and $$S_2O_3^{-2}$$ ions

3 g of a salt of molecular weight 30 is dissolved in 250 g of water. The molality if the solution is _____.