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

`HNO_(3)` acts as a powerful oxidising agent along with acting as acid. In this case, hydrogen gas which is intially involved is oxidised to water.
`Zn + 2HNO_(3) rarrZn(NO_(3)) + 2H`
`(HNO_(3) + H rarr H_(2)O + NO_(2)xx2)/(Zn + 4HNO_(3) rarr Zn(NO_(3))_(2) + 2NO_(2) + 2H_(2))`