Compounds

Question 8 • AA-F26 Physical Science

Which statement correctly describes why a compound is a pure substance?

Answer

A compound is not a pure substance because each of its molecules is made up of the atoms of two or more different elements.

A compound is a pure substance because its molecule cannot be broken down into simpler particles by physical means.

A compound is not a pure substance because it is not an element, and only elements are pure substances.

A compound is a pure substance because it consists of two different elements, which are pure substances.

Explanation

A pure substance has a uniform, definite composition. A compound fits this description because its elements are chemically combined in fixed proportions, and the compound cannot be separated into simpler substances by physical methods. Choice B is correct; breaking a compound into its elements requires a chemical change, not a physical means.

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