What is the difference between pure substance, element, and compund

Pure substance- a material that has constant composition. It has distinct chemical properties.
Element- a substance that cannot be broken down into any other substances.
Compound- substance made up of two or more different elements.

Only one reactant yields 2 or more products. meaning you will only have 1 product and it will break down into 2 or more products. eg. h2o -> h2 + o2

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