Question:

Which of the following processes does not involve oxidation of iron?

Formation of Fe(CO)5 from Fe

Rusting of iron sheets

Liberation of H2 from steam by iron at high temperature

Decolourization of blue CuSO4 solution by iron

Solution:

During the transformation, Fe + 5CO → Fe(CO)5, the oxidation number of iron metal is 0. The oxidation number of iron in Fe(CO)5 is also 0 as CO is a neutral ligand having 0 oxidation number. There is no change in the oxidation number of iron. Iron is not oxidized. Hence, option A is correct.