1) an individual substance;
2) type of substance (simple or complex);
3) one molecule of a substance (for substances with a molecular structure), a formula unit (for substances with a non-molecular structure);
4) the qualitative composition of the substance, i.e. what chemical elements are included in its composition;
5) the quantitative composition of the substance, that is, the number of atoms of each chemical element in the composition of its one formula particle.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.