Iron, Oxygen and Hydrogen are examples of which kind of substance?

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Elements are pure substances that consist of only one kind of atom and cannot be broken down into simpler substances by chemical means. Iron, oxygen, and hydrogen fit this definition because each is a single type of atom. In nature, oxygen and hydrogen often exist as diatomic molecules (O2 and H2), but they remain elements—still composed of only one kind of atom. This distinguishes them from compounds, which are formed when two or more elements are chemically bonded to create a new substance, and from mixtures or solutions, which are physical blends of different substances not chemically bonded.