Which condition(s) are necessary for the formation of dew?

The formation of dew is primarily dependent on specific atmospheric conditions, particularly relating to temperature and humidity. For dew to form, the air must become saturated, meaning it has reached its dew point, which is the temperature at which the water vapor in the air condenses into liquid water.

When the Earth's surface cools, especially during the night under clear skies, it allows the air directly in contact with the surface to cool as well. If this surface temperature drops below the dew point of the air, condensation occurs, resulting in dew formation. Calm air aids the cooling process and allows the surface temperature to drop more significantly. Thus, the combination of clear skies (which allow for radiative cooling), calm air (which helps prevent mixing of warmer air), and the surface being cooler than the dew point are critical for dew to form.

Other conditions may not effectively contribute to dew formation. Humidity alone without the necessary cooling and stable conditions will not lead to dew. Therefore, the specific combination of factors in the correct choice is essential in understanding how dew is formed.