6. Chemical Quantities & Aqueous Reactions

When a(n) _________ agent oxidizes, it causes reduction in another substance.

Which element is being reduced in the following reaction? 

Cr₂O₇^2- + 3 HNO₂ + 5 H⁺ → 2 Cr³⁺ +  3NO₃^- + 4 H₂O