Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg), are treated with `HNO_(3)`, hydrogen is not liberated, why ?

Explanation

When metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg) are treated with `HNO_(3)` hydrogen is not liberated because Nitric acid `(HNO_(3))` is a strong oxidising agent. Thus, 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 `NO_(2)` or NO or `N_(2)O`. So, in the reaction of metals (except Mn and Mg) with dilute nitric acid, no hydrogen gas is evolved.