How does air density generally change with increasing altitude?

How does air density generally change with increasing altitude?

• A. Increases
• B. Remains constant
• C. Varies unpredictably with altitude
• D. Decreases

Answer: (D)

The main idea is that air density decreases as altitude increases because the atmosphere becomes thinner the higher you go. Density is the mass of air per unit volume, and as you climb, there are fewer air molecules packed into each cubic meter. This happens because the weight of the air above decreases with altitude, leading to lower pressure. According to the ideal gas relationship ρ = P/(R T), the drop in pressure with height generally outweighs temperature effects, so the number of molecules per unit volume falls. That’s why air at higher elevations is less dense. The other options don’t fit because air isn’t increasing in density with height, it isn’t constant everywhere, and while there are temperature layers that can alter density locally, the overall trend is a decrease.

The main idea is that air density decreases as altitude increases because the atmosphere becomes thinner the higher you go. Density is the mass of air per unit volume, and as you climb, there are fewer air molecules packed into each cubic meter. This happens because the weight of the air above decreases with altitude, leading to lower pressure. According to the ideal gas relationship ρ = P/(R T), the drop in pressure with height generally outweighs temperature effects, so the number of molecules per unit volume falls. That’s why air at higher elevations is less dense. The other options don’t fit because air isn’t increasing in density with height, it isn’t constant everywhere, and while there are temperature layers that can alter density locally, the overall trend is a decrease.