Concept:The wet bulb cools by evaporation only when the surrounding air can absorb more moisture.
Explanation:When the air is dry, evaporation from the wet bulb is rapid, causing its temperature to fall below the dry bulb temperature.
If the air is already saturated, it cannot hold any more moisture.
Therefore, no evaporation occurs from the wet bulb.
As a result, both the wet and dry bulb thermometers record the same temperature.
This condition means the relative humidity is 100%, so the air is fully saturated.
Answer:B. air is saturated