Answer: Cooking gas is a Mixture
Step-by-step explanation:
A pure substance is a substance which contains definite composition of only one type of component. Hence, it cannot be separated by physical means.
On the other hand, a mixture is a substance which contains two or more than two types of components and they can be separated by physical means as well.
Cooking gas is a made up of a combination of different hydrocarbons (methane, ethane , butane etc) and thus is a mixture.