Substances can be classified as either element, compound or mixtures. Elements are the purest form of substances, since they contain only one type of atoms. Examples of elements include, iron, silver, gold, copper, etc. Compounds are formed when two or more elements combine in a fixed ratio, in such a manner that the final product has different properties than its individual components. An example of a compound is water (H2O) which is formed by combination of hydrogen and oxygen in a fixed 2:1 ratio. Mixtures are formed by a combination of two or more elements or compounds in a non-specific ratio.
Wood is a mixture and consists of various components such as lignin, cellulose, etc. The relative concentration of these components is not fixed and hence wood can be classified as a mixture. In fact, wood can be termed a heterogeneous mixture.
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