Question

5 what is the main idea of this text?
a air pressure is the same in the international space station as in the earth’s surface because the density of air is maintained in the station.

b air pressure in a container can be increased by adding molecules or heat, and it can be decreased by subtracting molecules or heat.

c air pressure on earth decreases as elevation increases because the number of molecules decreases with height.

d air pressure is observed by the exerted force of atoms and molecules, and it can be changed by adding or subtracting molecules or heat.

Explanation:

To determine the main idea about air pressure, we analyze each option:

• Option A: Compares air pressure in space station and Earth’s surface, but this is a specific case, not the main idea about air pressure in general.
• Option B: Discusses changing air pressure in a container, which is a specific scenario (container - based), not the overarching main idea.
• Option C: Explains that as elevation (height) increases on Earth, air pressure decreases because the number of air molecules decreases. This is a fundamental and general concept about air pressure's relationship with elevation on Earth, which is a key main idea about air pressure.
• Option D: Talks about changing air pressure by adding/subtracting molecules or heat, which is about manipulation, not the core main idea of air pressure's behavior with elevation etc.

Answer:

C. Air pressure on Earth decreases as elevation increases because the number of molecules decreases with height.