CBSE Class 9 Answered

When the temperature drops at night, it causes the moisture to condense, thus creating fog, due to a drastic temperature difference. Fog is neither water vapour nor gas, it is water condensed upon microscopic dust particles. For a given absolute humidity level, there is a temperature below which the water vapor in the air condenses onto any equally cool or cooler surface. This is called the dew point. If the temperature goes back up, like after sunrise, then it passes above the dewpoint and the condensed water evaporates, causing the fog to disappear.