Why is air considered a mixture and not a compound?

Air is considered a mixture because it exhibits the following properties:
1. Each component present in the air retains its properties.
2. Each component can be separated by simple physical processes.
3. The components do not have any fixed proportions. All gases are present in different
amounts. For example, in greener areas—more oxygen and water vapor are present; near the industrial area—air consists of a lot of impurities and smoke suspended in it.

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