Question

Specify a metal that liberates ${\mathrm{H}}_2$ gas with dilute Nitric acid.

Answer 1

1. Metals do not liberate Hydrogen (${\mathrm{H}}_2$) gas with Nitric acid (${\mathrm{HNO}}_3$) because Nitric acid is a strong oxidizing agent, so as soon as Hydrogen gas is formed in the reaction between a metal and dilute Nitric acid, the Nitric acid oxidize this Hydrogen to Water.
2. Hence, Magnesium($\mathrm{Mg}$) and Manganese($\mathrm{Mn}$) are the only two metals which liberate Hydrogen gas with very dilute Nitric acid.

$$\begin{gathered} \mathrm{Mg}\left(\mathrm{s}\right)+2{\mathrm{HNO}}_3\left(\mathrm{aq}\right)\to \mathrm{Mg}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \left(\mathrm{Magnesium}\right)(\mathrm{Nitric}\mathrm{acid})(\mathrm{Magnesium}\mathrm{nitrate})(\mathrm{Hydogen}\mathrm{gas}) \end{gathered}$$

$$\begin{gathered} \mathrm{Mn}\left(\mathrm{s}\right)+2{\mathrm{HNO}}_3(\mathrm{aq})\to \mathrm{Mg}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \left(\mathrm{Manganese}\right)(\mathrm{Nitric}\mathrm{acid})(\mathrm{Magnesium}\mathrm{nitrate})(\mathrm{Hydogen}\mathrm{gas}) \end{gathered}$$

Therefore, the metals which react with Nitric acid to liberate ${\mathrm{H}}_2$ gas are Magnesium($\mathrm{Mg}$) and Manganese($\mathrm{Mn}$).