Question

Nitric acid is not used for the preparation of hydrogen from metals. why?

Answer 1

1. Nitric acid$\left({\mathrm{HNO}}_3\right)$ is not used for the preparation of hydrogen from metals because it is a strong oxidizing agent.
2. It oxidizes the dihydrogen gas produced during the reaction with metals to Water.

For example

When zinc reacts with nitric acid it forms zinc nitrates, nitrogen oxide, and water.

$3\mathrm{Zn}+\underset{\mathrm{Nitric}\mathrm{acid}}{8{\mathrm{HNO}}_3}\to \underset{\mathrm{Zinc}\mathrm{nitrate}}{3\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2}+\underset{\mathrm{Nitrogen}\mathrm{oxide}}{4\mathrm{NO}\left(\uparrow \right)}+2{\mathrm{H}}_2\mathrm{O}$

That is why nitric acid is not used for the preparation of hydrogen gas from the metal