The correct answer is option 4: our perspiration evaporates rapidly.

When we feel hot, our body sweats in order to regulate its temperature. Sweat is made up of water and salts, and as it evaporates from our skin, it cools us down because the process of evaporation requires energy, which is taken from the surrounding heat.

When a fan is turned on, it creates air movement around us, which increases the rate of evaporation of sweat from our skin. This rapid evaporation helps to cool us down faster, leading to a feeling of comfort during hot weather.

Options 1, 2, and 3 are incorrect explanations for why a fan produces a feeling of comfort during hot weather. Our body radiates heat regardless of the presence of a fan, and a fan does not supply cool air but rather moves the existing air. Additionally, the conductivity of air does not affect the cooling effect of a fan.