Hydrogen gas is usually liberated when an acid reacts with a metal.
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Take few pieces of zinc granules and add 5 ml of dilute \\( \\mathrm { H } _ { 2 } \\mathrm { SO } _ { 4 } \\). Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
\\( 2 \\mathrm { H } _ { 2 } \\mathrm { SO } _ { 4 } + \\mathrm { Zn } \\longrightarrow \\mathrm { Zn } \\left( \\mathrm { SO } _ { 4 } \\right) _ { 2 } + 2 \\mathrm { H } _ { 2 } \\uparrow\\)
we can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.