when is thhe sample of matter considered as a pure substance?

Answer 1

A pure substance can be either 1.) an element or 2.) a compound.

Elements are the simplest form of matter, and are what you see in the periodic table.

Compounds are chemical combinations of two or more elements.

Answer 2

pure means that nothing further can be seperated by physical means, such as boiling, filtering, etc.

Answer 3

When it has only one chemical entity in it, like carbon, oxygen, H2O (water) etc.