In the rusting of iron, 4Fe + 3O2 ---> 2Fe2O3, how many electrons are exchanged and which element is oxidized?

Answer 1

In the reaction, valence of Fe changes from 0 to +3 in Fe2O3, O changes from 0 to -2. Multiple the moles for either element, exchanged electrons=4*3 or 2*6=12.

Valence increasing for oxidation, decreasing for reduction. So Fe is oxidized and O is reduced.