Before revision: Examples of naturally occurring free elements include the oxygen molecule (O) and carbon.Chemistry of the Elements (Second Edition) A. Earnshaw and Norman Greenwood ISBN: 978-0-7506-3365-9 Mentions "free element" 30 times, for example "Carbon occurs both as a free element and in combined form."
After revision: Examples of elements which can occur as free elements include the oxygen molecule (O) and carbon.Chemistry of the Elements (Second Edition) A. Earnshaw and Norman Greenwood ISBN: 978-0-7506-3365-9 Mentions "free element" 30 times, for example "Carbon occurs both as a free element and in combined form."