Which of the following shows that air is a mixture?

I. It has varied composition from place to place. II. Its constituents can be separated by physical means. III. It contains unreactive noble gases.

Correct answer: I and II only.

Explanation:

• I. Varied composition – Mixtures can have compositions that change from place to place and time to time (e.g., humidity, CO₂ level, pollutants). This supports that air is a mixture.
• II. Separable by physical means – Components of air (N₂, O₂, Ar, etc.) can be separated by physical processes like fractional distillation of liquefied air. This also shows it is a mixture.
• III. Contains unreactive noble gases – True, but the presence of noble gases alone doesn’t prove the mixture nature; it’s just a fact about its composition, not an indicator of being a mixture.