Final answer:
A compound is a substance with two or more elements, molecules of compounds have multiple types of atoms, alloys are homogeneous mixtures of metals, salt is an ionic compound with positive and negative ions.
Step-by-step explanation:
A compound is a substance that consists of two or more elements in a unique composition. The smallest particle of a compound is called a molecule. Chemical bonds hold together the atoms of molecules. Molecules of compounds contain two or more types of atoms, while molecules of elements contain only one type of atom.
An alloy is a solid solution or homogeneous mixture of two or more elements, where at least one element is a metal. Alloys often have properties that are different from those of their constituent elements. For example, bronze is an alloy of copper and tin, which has different properties from pure copper or tin.
A salt, also known as an ionic compound, is composed of positive ions (cations) and negative ions (anions) held together by ionic bonds. An example of a salt is table salt, which is made up of sodium ions (Na+) and chloride ions (Cl-).