CBSE Notes for Is Matter Around Us Pure Class 9 Extra Questions
In terms of matter, as per scientists the best way to determine if a substance is pure or not is to take a part of that substance from one portion and compare it to another part of that very substance obtained from another random portion. They should match and there should be no discrepancy.
One can say that a pure substance is that which is made of a single element or only one kind of molecules.
CBSE Revision Notes 