To prove that the evolved gas is hydrogen, do the following:
1. Take dilute hydrochloric acid or dilute sulphuric acid in a test tube.
2. Take a small metal piece(iron nail) and put it in the test tube.
3. You will see small bubbles of gas coming out of the acid. Close the mouth of the test tube by your thumb so that the gas remains inside.
4. Bring a burning match stick to the mouth of the tube and remove your thumb.
5. The match stick will extinguish with a pop sound which confirms that the gas produced is hydrogen.