Question

differentiate between fog and dew

Answer 1

FOG ­ Fog is a cloud which is in contact with the ground. Much like clouds in the sky, fog forms when the air becomes supersaturated, meaning that it can no longer hold moisture in the form of vapor. As a result, water precipitates out of the air, forming a fine mist of water droplets.
Dew ­ Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at which it can evaporate resulting  in formation of water droplets

Answer 2

Fog is a substance, which is formed by the combination of both water vapour and the dust particles.
Dew is the pure form of water vapour formed on cold substances.