Question

which best describes an element? a type of a mixture; a pure compound; an impure substance; a pure substance

Explanation:

1. Analyze "a type of a mixture": Elements are not mixtures. Mixtures are combinations of two or more substances, while elements are pure substances made of only one type of atom. So this is incorrect.
2. Analyze "a pure compound": A compound is made of two or more different elements chemically bonded. An element is not a compound, so this is incorrect.
3. Analyze "an impure substance": Elements are pure substances (they have a definite and constant composition of only one type of atom). So this is incorrect.
4. Analyze "a pure substance": An element is a pure substance because it consists of only one kind of atom and has a fixed composition. For example, oxygen (O₂) or gold (Au) are elements and pure substances.

Answer:

D. a pure substance (assuming the last option is labeled D; if the labels are different, adjust the label but keep the text "a pure substance")