Name the following:
A metal which liberates nitric oxide and nitrogen dioxide with nitric acid under different conditions.

• Copper $\left(\mathrm{Cu}\right)$ reacts with cold dilute nitric acid $\left({\mathrm{HNO}}_3\right)$ to produce nitric oxide $\left(\mathrm{NO}\right)$ as a gas. The reaction is as follows:
  $\underset{\mathrm{copper}}{3\mathrm{Cu}\left(\mathrm{s}\right)}+\underset{\mathrm{nitric}\mathrm{acid}}{8{\mathrm{HNO}}_3(\mathrm{aq}.)}\to \underset{\mathrm{copper}\mathrm{nitrate}}{3\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2(\mathrm{aq}.)}+\underset{\mathrm{water}}{4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{nitric}\mathrm{oxide}}{2\mathrm{NO}\left(\mathrm{g}\right)}$
• Nitrogen dioxide $\left({\mathrm{NO}}_2\right)$ is released when hot nitric acid reacts with copper: The reaction is as follows:
  $\mathrm{Cu}\left(\mathrm{s}\right)+4{\mathrm{HNO}}_3\left(\mathrm{aq}\right)\to \mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+2{\mathrm{NO}}_2\left(\mathrm{g}\right)$
• Thus, copper is the metal which liberates nitric oxide and nitrogen dioxide with nitric acid under different conditions.