Explanation:
Air is a mixture of gases, mainly nitrogen (78%) and oxygen (21%). It has a mass and occupies space. The density of air is defined as the mass of air per unit volume of air. The density of air can change with different factors like temperature, pressure, and humidity.

Factors affecting the density of air:
There are three major factors that affect the density of air. These are:

1. Temperature: When the temperature of air increases, its molecules move faster and occupy more space. This results in a decrease in air density. Conversely, when the temperature decreases, the molecules slow down and occupy less space, resulting in an increase in air density.

2. Pressure: Air density also changes with pressure. As the pressure increases, the molecules of air move closer together, resulting in an increase in air density.

3. Humidity: The amount of water vapor in the air affects its density. Moist air is less dense than dry air at the same temperature and pressure.

Density of air with height:
As we move higher in the atmosphere, the air pressure decreases. This is because the weight of the air above decreases as we move higher. As a result, the air molecules spread out and occupy more space. This results in a decrease in air density with height. The density of air decreases at a rate of approximately 1% per 100 m of altitude. This means that the air is less dense at higher altitudes than at lower altitudes.

Conclusion:
In conclusion, the density of air decreases with height. This is because the pressure decreases with height, causing the air molecules to spread out and occupy more space.

The density of air decreases with height. There are two reasons: at higher altitudes, there is less air pushing down from above, and gravity is weaker farther from Earth's center. So at higher altitudes, air molecules can spread out more, and air density decreases .