Which half-reaction correctly represents reduction?
A. Cr3+ + 3e- -> Cr(s).
B. Cr3++ -> Cr(s) + 3e-.
C. Cr(s) -> Cr3+ + 3e-.
D. Cr(s) + 3e- -> Cr3+.
E. Cr + 3e- -> Cr4+.
In reduction half reactions, the oxidation number is lowered because electrons are added. When Cr3+ gains electrons, the negative charge of the electron cancels out the positive charge and an uncharged Cr (Cro) atom results.