Which of the following cannot be classified as a substance? gold table salt nitrogen air description

Air

Explanation:

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: table salt

Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Gold  , nitrogen

Mixture is defined as a composition which has two or more components which do not combine chemically and do not have any fixed ratio in which they are present. Example: Air

they include patterns; cause and effect; scale, proportion, and quantity; systems and system models; energy and matter; structure and function; and stability and change.

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