Which statement best defines an element?

Which statement best defines an element?

• A. A substance that cannot be broken down into simpler substances by chemical means
• B. A substance consisting of two or more elements
• C. A substance that is always a compound
• D. A substance with a variable composition

Answer: (A)

An element is a pure substance made of one type of atom that cannot be broken down into simpler substances by chemical means. That single-atom identity is what keeps an element from being decomposed into other substances through ordinary chemical reactions; any such decomposition would produce a substance with different atoms, which would be a compound or a mixture, not an element. So the statement that captures this idea is the one describing a substance that cannot be reduced to simpler substances by chemical means. The other descriptions describe substances that are made of two or more elements (compounds) or mixtures with variable composition, which are not elements. (Note that elements can exist as single atoms or as diatomic molecules, but they are still not broken down into different substances by chemical processes.)

An element is a pure substance made of one type of atom that cannot be broken down into simpler substances by chemical means. That single-atom identity is what keeps an element from being decomposed into other substances through ordinary chemical reactions; any such decomposition would produce a substance with different atoms, which would be a compound or a mixture, not an element.

So the statement that captures this idea is the one describing a substance that cannot be reduced to simpler substances by chemical means. The other descriptions describe substances that are made of two or more elements (compounds) or mixtures with variable composition, which are not elements. (Note that elements can exist as single atoms or as diatomic molecules, but they are still not broken down into different substances by chemical processes.)