Cr₂O₇^2-_(aq) + 14H⁺_(aq) + 6l^-_(aq) → 2Cr³⁺_(aq) + 3l_(g) + 7H₂O_(I).
The change in the oxidation number of oxygen in the equation above is?

• A.0
• B.1
• C.2
• D.7
• E.