ANS:B - gases

Dry air refers to air that contains no water vapor. It is composed primarily of gases, including nitrogen, oxygen, argon, carbon dioxide, and traces of other gases. So, dry air is a mixture of gases. The term "vapors" typically refers to substances in the gas phase that are usually liquids or solids at room temperature and atmospheric pressure, such as water vapor. While air can indeed contain water vapor, "dry air" specifically refers to air without water vapor. Therefore, the correct answer is "neither (a) nor (b)." Dry air is a mixture of gases only.