If condensation occurs on a window, which two conditions must be true?

For condensation to occur on a window, the surface temperature of the window must be below the dew point of the surrounding air. The dew point is the temperature at which moisture in the air begins to condense into liquid. Therefore, if condensation forms on the window, it indicates that the window surface is below the dew point temperature of the air inside the room. Additionally, there must be moisture present in the air; without moisture, condensation cannot happen.

Thus, the correct scenario is that the window surface is below the dew point, and there is indeed moisture in the air to condense. This aligns with the process of condensation, where excess humidity in the air encounters a cooler surface, causing the moisture to turn from vapor to liquid, creating the visible droplets on the window.