Aluminum is classified as a pure substance.
A pure substance consists of only one type of material with consistent properties throughout. In the case of aluminum, it is a chemical element with the symbol ‘Al’ and atomic number 13. It cannot be separated into different substances by physical means.
On the other hand, a heterogeneous mixture contains two or more different substances that can often be physically separated, like a salad or a rock mixture. Solutions are homogeneous mixtures where one substance is dissolved in another, such as saltwater.
Since aluminum maintains the same composition and properties throughout its entire structure, it is not a mixture or solution, but a pure substance.