Correct Option
The correct option is (c).
Explanation
Air is the invisible mixture of gases that surrounds the Earth, forming the atmosphere. It possesses physical properties such as mass, density, and pressure, which are influenced by gravity and altitude.Statement 1 is Incorrect: Air is not a single element or a chemical compound. It is a mechanical mixture of various gases. The primary constituents are Nitrogen (approximately 78%) and Oxygen (approximately 21%), along with Argon, Carbon Dioxide, water vapour, and trace gases. These gases retain their individual properties within the mixture.
Statement 2 is Correct: Air has mass, and consequently, it exerts pressure. As a fluid, air exerts atmospheric pressure in all directions-upwards, downwards, and sideways. This pressure is the result of the weight of the air column pressing down on objects and surfaces.
Statement 3 is Correct: The density of air is not uniform throughout the atmosphere. Due to the Earth's gravitational pull, air molecules are concentrated near the surface. Consequently, air is densest at sea level, and the density decreases rapidly with an increase in altitude.
Key Takeaway: Air is a mixture of gases, not a single element. Its physical behavior follows fluid dynamics, exerting pressure in all directions, with density being highest at sea level due to gravitational compression.