Asubstance is either an element or a solution, compound, heterogeneous mixture, or homogenous?

For better understanding:

Chemical element is represented by a symbol.
Solution is any homogeneous mixture.
Chemical substance is represented by a formula.
 
The substances in whose formulas only appear atoms of a chemical element are called simple substances. When there are atoms of more than one chemical element, it is a compound substance or chemical compound. Mixture is a system made up of two or more pure substances, called components.
The mixtures can be classified as homogeneous and heterogeneous. The difference between them is that the homogeneous mixture is a solution that presents a single phase while the heterogeneous can present two or more phases.

Variables,control,conclusion and finally scientific theory