Matter is defined as anything that has mass and occupies space, it may be classified into three states, solid, liquids or gases. Molecules is the smallest particle of an element that has the chemical properties of the element or the compound. it contains two or more atoms that are joined together. A pure substance is a matter that has distinct properties and a composition that does not vary from sample to sample. Thus the correct answer is C
Pure substance is any substance formed by only one type of molecule, of invariable and homogeneous chemical composition, which has constant physical and chemical properties. Pure substance may exist in more than one phase, but in such cases the phase composition will be the same.
In short, pure substance is all material with the following characteristics:
Structural units (molecules, ionic assemblies) chemically equal to each other.
Fixed composition, resulting in fixed properties such as density, melting and boiling point, etc. That is, these substance have distinct properties and composition that never vary.
The temperature remains unchanged from the beginning to the end of all your physical state changes (melting, boiling, solidifying, etc.).
