Which of the following metals produces hydrogen gas on reacting with cold dilute nitric acid?
Which of the following metals produces hydrogen gas on reacting with cold dilute nitric acid?
$\mathrm{Al}$
$\mathrm{Fe}$
$\mathrm{Mg}$
$\mathrm{Cu}$
Solution
Both magnesium $(\mathrm{Mg})$ and manganese $(\mathrm{Mn})$ react with very dilute cold $\mathrm{HNO}_3$ to evolve $\mathrm{H}_2$ gas. Magnesium metal reacts with dilute nitric acid to form magnesium nitrate and hydrogen gas
$
\mathrm{Mg}+\underset{\begin{array}{c}
\text { Cold and } \\
\text { dilute }
\end{array}}{2 \mathrm{HNO}_3} \longrightarrow \underset{\begin{array}{c}
\text { Magnesium } \\
\text { nitrate }
\end{array}}{\mathrm{Mg}\left(\mathrm{NO}_3\right)_2}+\mathrm{H}_2(g)
$
Hydrogen gas is not evolved when other metals react with nitric acid because it is a strong oxidising agents. It oxidises hydrogen produced to water and itself gets reduced to nitrogen oxide