* Compound: A substance formed when two or more different elements are chemically bonded together. Water (H₂O) is made of two hydrogen atoms and one oxygen atom bonded together.

* Mixture: A combination of two or more substances that are not chemically bonded. Mixtures can be separated by physical means.

* Element: A pure substance that cannot be broken down into simpler substances. Hydrogen and oxygen are elements.

* Solution: A type of mixture where one substance (solute) is dissolved evenly into another substance (solvent). Water can be a solvent, but it is still a compound itself.

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