Answer
A reaction in which there is an evolution of a gas is called gas-evolution reaction.
Work Step by Step
A gas evolution reaction is a reaction in which one of the products formed is a gas.
Example- In the reaction of sulfuric acid with calcium carbonate, the products formed are calcium sulphate, water and carbon dioxide (gas).
$CaCO_{3} + H_{2}SO_{4} = CaSO_{4} + H_{2}O + CO_{2}$
Here $CO_{2}$ is liberated as a gas.
