4. What best describes the density of the atmosphere? A. It increases as you increase in altitude B. It decreases as you increase in altitude C. It maintains a constant level throughout the atmosphere D. It shows fluctuations up and down as you move through the layers of the atmosphere E. It does not change

B.

Air pressure decreases as you increase in altitude.

Explanation:

Gravity pulls the gas molecules towards the center of the earth. This pull of gravity becomes stronger and closer to the center at sea level. Air becomes dense at sea level where the gravitational pull is stronger. Gases at the sea level are also compressed by the weight of the atmosphere above them. The force of the earth weighing down over a unit air is known as atmospheric pressure. At higher altitudes, the atmospheric pressure is lower and the air is less dense than at higher altitude.