This equation represents the reaction of copper with concentrated nitric acid. $\text{Cu}(s) + 4\text{HNO}_3(aq) \rightarrow \text{Cu(NO}_3\text{)}_2(aq) + 2\text{NO}_2(g) + 2\text{H}_2\text{O}(l)$. Which element undergoes reduction in this reaction?
- Aoxygen
- Bnitrogen
- Ccopper
- Dhydrogen