Define the term pure substance​

Pure substances are substances that are made up of only one kind of particles and has a fixed or constant structure. Pure substances are further classified as elements and compounds. An element is a substance that consists of only one type or kind of atom

define the term pure substance​ :

A pure substance does not have to be of a single element or compound, This can either be one single element or one single compound, but every sample of this substance that you examine must contain exactly the same thing with a fixed, definite set of properties

Explanation:

the temperature of the gas, in k, not celsius.