Concept:The troposphere is the lowest atmospheric layer, and it is the layer where temperature generally decreases with an increase in altitude.
Explanation:The Earth's surface absorbs sunlight and heats up, warming the air directly above it.
This warm air rises and expands, causing it to cool as it moves upward.
Therefore, the air closer to the ground is warmer than the air at higher altitudes.
This pattern of decreasing temperature with height is a defining feature of the troposphere.
In contrast, the stratosphere warms with height because the ozone layer absorbs ultraviolet radiation.
The ionosphere and exosphere also behave differently, with temperatures that can rise due to solar radiation.
Thus, among the given options, the troposphere is the layer where temperature falls as altitude increases.
Answer:B. troposphere