Radiation Safety Practice Exam

Which of the following is a pure substance that cannot be broken down into simpler substances by chemical means?

1. Mixture

2. Element

3. Compound

4. Solution

The correct answer is: Element

The correct answer is an element, which is defined as a pure substance that cannot be broken down into simpler substances by chemical means. Elements consist of only one type of atom and are the fundamental building blocks of matter. Each element retains its unique properties and cannot be transformed into a simpler substance without changing its inherent nature. For instance, consider the periodic table—each entry represents a different element, such as hydrogen or oxygen. These elements are pure substances; they can combine chemically to form compounds but cannot be decomposed into anything simpler by chemical reactions. This property distinguishes elements from compounds, which are substances formed from two or more elements that are chemically bonded together. Compounds can indeed be broken down into their elemental components through chemical reactions. Mixtures and solutions, on the other hand, consist of two or more substances physically combined but retaining their individual properties. These can often be separated back into their original components without any chemical change occurring. Therefore, they do not qualify as pure substances in the same way that elements do. This makes the element the correct choice for identifying a substance that cannot be chemically deconstructed into simpler forms.