The volume, in mL, of 0.02 M K₂Cr₂O₇ solution required to react with 0.288 g of ferrous oxalate in acidic medium is _______.
(Molar mass of Fe = 56 g mol^–1)

A 100 mL solution was made by adding 1.43 g of Na₂CO₃.xH₂O. The normality of the solution is 0.1 N. The value of x is _____.

(The atomic mass of Na is 23 g/mol)

The oxidation states of transition metal atoms in K₂Cr₂O₇, KMnO₄ and K₂FeO₄, respectively, are x, y and z. The sum of x, y and z is _______.