state three reasons why you think air is a mixture and water is a compound.

Explanation

The justification can be done on the basis of the following points in its supports.
1. The composition of air is not always the same. At high altitudes, the percentage of oxygen decreases. Similarly, in industrial towns, we normally say that the air is more polluted. This means that the percentages of carbon monoxide, sulphur dioxide and other poisonous gases in air has increased.
2. The major constituents of air can be easily separated by physical methods such as liquefaction, fractional distillation etc. We shall discuss these methods a little later in the present chapter.
3. The different gases present in air do not lose their identities. For example, air supports combustion which means that it contains oxygen. Similarly, air turns lime water milky. This establishes the presence of carbon dioxide in air.
4. No energy changes or no chemical reactions occur when the constituents of air are tried to be mixed.
All these evidences support the fact that air is a mixture and not a compound.