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

Hydrogen gas is usually liberated when an acid reacts with a metal.

For example: When zinc granules react with dilute sulphuric acid, then hydrogen gas is liberated and zinc sulphate solution is formed.

The evolved hydrogen gas can be tested by taking a burning candle near gas filled bubbles. If candle burns with pop sound, it confirms the evolution of hydrogen gas.