The correct answer is option 2: always a mixture.

Auiris is described as a mixture because it refers to a combination of different substances that are not chemically bonded together. Mixtures can be made up of elements, compounds, or a combination of both. The substances in a mixture can be easily separated through physical means, such as filtration or evaporation.

Option 1 suggests that Auiris is always a compound. However, this is incorrect because compounds are substances that are made up of two or more elements chemically bonded together.

Option 3 states that Auiris is a compound in pollution-free zones. This option is not accurate because the environmental conditions, such as pollution, do not change the chemical composition of a substance. Auiris would still be a mixture regardless of the presence or absence of pollution.

Option 4 suggests that Auiris is a mixture in industrial zones. This option is incorrect as well because the location or industrial activity does not determine the classification of Auiris. Auiris is always a mixture regardless of the environment it is found in.

In summary, Auiris is correctly classified as a mixture because it is a combination of different substances that can be separated through physical means.