Radiation Safety Practice Exam

A substance composed of different elements bound in fixed proportions is defined as a compound. Compounds are formed when two or more elements chemically bond together in specific ratios, resulting in a unique substance with distinct properties that differ from the individual elements.

For example, water (H2O) is a compound made from two hydrogen atoms and one oxygen atom. The fixed proportion of these atoms is essential to the chemical identity and characteristics of water.

In contrast, an element consists of a single type of atom and cannot be broken down into simpler substances. A mixture contains two or more substances that retain their individual properties and can vary in proportions, so they do not have fixed ratios. An alloy is a specific type of mixture, typically of metals, that may have varying proportions of its components and does not constitute a compound in the strict sense. Thus, a compound is distinguished by its fixed composition, which is why it is the correct answer.