1. Variable Composition:
* Mixtures have variable compositions: The proportions of gases in air can change depending on location, altitude, and other factors. For example, air in a city will have higher levels of pollutants than air in a remote forest.
* Compounds have fixed compositions: Water (H₂O) always has a fixed ratio of two hydrogen atoms to one oxygen atom, regardless of where it is found.
2. No Chemical Bonding:
* Mixtures are formed by physically combining substances: The gases in air are simply mixed together, and there are no chemical bonds holding them together.
* Compounds are formed by chemically bonding atoms: The atoms in a compound are held together by chemical bonds, which are strong forces of attraction between atoms.
3. Separation by Physical Means:
* Mixtures can be separated by physical means: The components of air can be separated by techniques like fractional distillation, where the different gases are boiled off at different temperatures.
* Compounds can only be separated by chemical reactions: To separate a compound into its constituent elements, a chemical reaction must be performed.
In summary: Air is a mixture because its components are not chemically bonded, the proportions of its components can vary, and it can be separated by physical means.
