Final answer:
A substance made from two or more types of atoms bonded in a specific ratio with properties different from its constituent atoms is a compound.
Step-by-step explanation:
The question refers to a substance where two or more types of atoms are bonded together in a specific ratio that does not change, and the properties of such a substance may be different from the properties of the atoms that comprise it. This description fits the definition of a compound. Compounds are made up of atoms of different elements that are chemically combined in fixed proportions. An example of a compound is water (H₂O), where two hydrogen atoms and one oxygen atom are bonded together in a specific arrangement, creating a substance with different properties from either oxygen or hydrogen alone.