In the Equation, C₄H₁₀(l)+ Cr₂O₇^2-(aq) + H⁺(aq) $\rarr$ H₆C₄O₄(s)+ Cr³⁺(aq)+ H₂O(l), the Change in the Oxidation Number of H₂O(l)

In the equation, C₄H₁₀(l) + Cr₂O₇^2-(aq) + H⁺(aq) $\rarr$ H₆C₄O₄(s) + Cr³⁺(aq) + H₂O(l) , the change in the oxidation number of the chromium atom is

A) a decrease by six units.
B) a decrease by three units.
C) an increase by three units.
D) an increase by five units.
E) an increase by eight units.