A compound is a substance composed of two or more different types of _____ chemically combined in a fixed proportion.
A substance that is composed of two or more elements, chemically combined with one another in a fixed proportion is called a ____.
The substance that is composed of two or more elements chemically combined with one another in a fixed proportion of mass is called ___ .
What do we call the substance which is composed of two or more elements, and chemically combined in a fixed ratio by mass?