The Tropopause ranges from 20,000 to 45,000 feet in altitude.

• A. It marks the boundary between the stratosphere and mesosphere.
• B. It is the layer with the lowest temperatures in the atmosphere.
• C. It ranges from 20,000 to 45,000 feet in altitude.
• D. It is where the air density is highest.

Answer: (C)

The Tropopause is the boundary between the troposphere, where weather happens, and the stratosphere above it, where the temperature trend changes from cooling with height to a more stable or warming profile. This change in the temperature gradient is what defines the tropopause, and it’s the altitude where most of the atmospheric mass that drives weather sits below it.

Altitude-wise, this boundary isn’t at a single fixed height. It varies with latitude and season, typically around 8–12 km (roughly 26,000–39,000 feet) at mid-latitudes and higher toward the equator. A broad way to express its range is about 20,000 to 45,000 feet, capturing the general variability you’d encounter in different locations. That’s why the statement saying it ranges from 20,000 to 45,000 feet is acceptable as a general description.

Other statements don’t fit the role of the tropopause: the boundary between the stratosphere and mesosphere is the stratopause, not the tropopause. The tropopause isn’t defined by having the lowest temperatures in the atmosphere—the upper layers of the atmosphere, like the mesosphere, can be colder. And air density is greatest near the Earth's surface, decreasing with altitude, so it isn’t the layer where density is highest.