ANS:A - Wet bulb temperature

The wet bulb temperature is a measure of the lowest temperature that can be reached by evaporating water into the air at constant pressure. It is determined by using a thermometer with its bulb wrapped in a wet cloth or wick, so that it is exposed to both the air and evaporating water. As the water evaporates from the cloth, it absorbs heat from the thermometer bulb and the surrounding air, causing the temperature indicated by the thermometer to decrease. The rate of evaporation and the resulting cooling effect depend on factors such as the humidity and air movement. The wet bulb temperature is significant in meteorology, HVAC (Heating, Ventilation, and Air Conditioning) systems, and other applications where the cooling effect of evaporation is important. It is often used in conjunction with the dry bulb temperature (the temperature measured by a regular thermometer) to calculate parameters such as relative humidity and dew point.