Question

when metals are treated with mineral acids they liberate hydrogen gas but when metals except magnese and magnesium are treated​ with nitric acid hydrogen gas is not liberated. Why?

Answer 1

Nitric acid (HNO3) is a strong oxidising agent. So, as soon as hydrogen gas is formed in the reaction between a metal and dilute nitric acid. The nitric acid oxidises this hydrogen to water and itself gets reduced to NO2 or NO orN2O. So, in the reaction of metals (except Mn and Mg) with dilute nitric acid, no hydrogen gas is evolved.

Answer 2

Heyya !

  Nitric acid or HNO₃ is a strong oxidizing agent.
  When an acid reacts with a metal , hydrogen gas is liberated.Here also , hydrogen gas is liberated. HNO₃  oxidises this hydrogen to water.
And , HNO₃ gets reduced to NO₂ ,N₂O  or NO