Oxidation states of the metal in the minerals haematite and magnetite, respectively are

For the first order reaction
2N₂O₅ (g) $$\to$$ 4NO₂ (g) + O₂ (g)

Consider the following cell reaction:
2Fe(s) + O₂(g) + 4H⁺(aq) $$\to$$ 2Fe²⁺ (aq) + 2H₂O (l); E^o = 1.67 V
At [Fe²⁺] = 10^-3 M, P(O₂) = 0.1 atm and pH = 3, the cell potential at 25^oC is

The freezing point (in ^oC) of a solution containing 0.1 g of K₃[Fe(CN)₆] (Mol. wt. 329) in 100 g of water (K_f = 1.86 K kg mol^-1) is