A student reacts $1\,\text{mol}$ of copper with concentrated nitric acid so that $1\,\text{mol}$ of copper(II) nitrate, $2\,\text{mol}$ of water and substance $X$ are produced. There is no additional product. Substance $X$ contains neither copper nor hydrogen. What might substance $X$ be?
- A$\text{N}_2$
- B$\text{N}_2\text{O}$
- C$\text{NO}$
- D$\text{NO}_2$