Which of the following is true about air?
A It is less dense than water.
B It has no density.
C It has the same density as water.
D It is denser than water.
The Correct Answer and Explanation is :
The correct answer is A. It is less dense than water.
Air is significantly less dense than water, which is why objects that are heavier than air, like a metal coin, sink in water but can move freely in the air. Density is defined as mass per unit volume, and the density of air is much lower than that of water because of the molecular composition and spacing between particles in gases versus liquids.
Why is Air Less Dense Than Water?
Air consists primarily of nitrogen (about 78%) and oxygen (about 21%), with smaller amounts of other gases like argon and carbon dioxide. In gases like air, the molecules are spread far apart, moving freely in all directions. This means that for a given volume of air, there are fewer molecules packed together compared to liquids or solids.
Water, on the other hand, is a liquid, and its molecules are much closer together due to stronger intermolecular forces. Water molecules have hydrogen bonds that keep them more tightly packed, giving water a higher density. This is why a cubic meter of water weighs much more than a cubic meter of air. The density of air at sea level and standard temperature is about 1.225 kg/m³, while the density of water is about 1,000 kg/m³. This stark difference explains why air is less dense than water.
Implications of Air’s Lower Density
The difference in density between air and water has practical effects in everyday life. For example, it explains buoyancy—boats float because they displace a volume of water that weighs more than the air inside them. It also plays a role in weather systems and flight, as airplanes rely on air’s lower density for lift.