question_answer 3)

               Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas? 

Answer:

Hydrogen gas is liberated when an acid reacts with a metal. For example, when zinc  metal reacts with dil.  hydrogen is evolved and salt zinc chloride is formed as:        It can be tested by bringing a burning candle near the gas. The candle continues burning with a pop sound.