Concept:A mixture has variable composition and its constituents can be separated by physical means.Explanation:Statement I shows air composition varies from place to place, which is a property of a mixture. Statement II shows air constituents can be separated by physical means, such as fractional distillation, which is also a property of a mixture. Statement III only states that air contains unreactive noble gases; it does not prove that air is a mixture.Answer:A. I and II only