Acids will react with metals to produce a salt and hydrogen gas.
Acid + Metal → Salt + Hydrogen
For example...
Magnesium + Hydrochloric Acid → Magnesium Chloride + Hydrogen Gas
Zinc + Sulphuric Acid → Zinc Sulphate + Hydrogen Gas
Copper + Nitric Acid → Copper Nitrate + Hydrogen Gas
To test whether a gas is hydrogen or not, collect it in a test tube by lacing your thumb over the neck. The gas can then be ignited. Hydrogen burns with a squeaky pop. This is sometimes called the 'pop test'.