* Variable Composition: The proportions of the gases that make up air can vary depending on location, altitude, and time. For example, air in a city will have more pollutants than air in a rural area.

* No Chemical Bonding: The gases in air are not chemically bonded together. They are simply physically mixed. This means that each gas retains its individual properties.

* Easy Separation: The components of air can be easily separated by physical means. For example, liquid nitrogen and oxygen can be obtained by fractional distillation of air.

In contrast, a compound is formed when two or more elements chemically combine in a fixed ratio. This results in a new substance with properties different from the original elements.

Here's a simple analogy: Imagine a bowl of fruit. The fruit is a mixture because each piece retains its individual properties (apple, orange, banana, etc.). You can easily separate the fruit by picking out each piece.

Air is similar. It's a mixture of different gases, each retaining its own properties, and these gases can be separated through physical means.