Water contains two parts hydrogen and one part oxygen (2 H and 1 O = H 2 O)
Because of this, the amount of hydrogen and oxygen produced during electrolysis of water is in a 2:1 ratio.
In electrolysis process, hydrogen goes to one test tube and oxygen goes to another. Because Water contains 2 part hydrogen, the amount of gas collected in one tube is double the amount collected in the other.
