Question

What occurs when Cr^3+ ions are reduced to Cr^2+ ions?

Answer 1

D:

When electrons are gained, the charge of the atom decreases.

When you are given an atom with a charge, the oxidation of that atom is the charge. So by going from a Cr^3+ (Oxidation Number = 3) to a Cr^2+ (Oxidation Number = 2), the Oxidation Number thus decreases.