The ratio of gases evolved during the electrolysis of water is 2:1, meaning for every two molecules of hydrogen gas (H₂), one molecule of oxygen gas (O₂) is produced.

Here's why:

* Electrolysis: This process uses electricity to break down water (H₂O) into its component elements: hydrogen and oxygen.

* Reaction: The overall reaction is: 2H₂O → 2H₂ + O₂

* Stoichiometry: The balanced chemical equation shows that two moles of water produce two moles of hydrogen gas and one mole of oxygen gas.

* Gas Volumes: Since the volume of a gas is directly proportional to the number of moles, the ratio of hydrogen to oxygen gas volumes is also 2:1.

Therefore, during the electrolysis of water, twice as much hydrogen gas is produced by volume compared to oxygen gas.