Which sample is a pure substance?

Explanation:

Matter is generally classified as either pure or impure substances.

 Pure substances are distinct substances with the following characteristics;

All parts are the same throughout which implies that they are homogenous Their composition is definiteThey cannot be easily separated or broken into simpler units by physical means. Separation by physical methods is not easy. They have a unique set of physical properties. These substances are elements and compounds.

Any substance that is an element or a compound is pure substance.

C) the increase in atmospheric pressure pushes the walls of the balloon outward thus making it  is the answer.hope i you.

The answer would be true