Most of the air in the lower troposphere at the equatorial low-pressure belt is

The correct answer is - warm and moist.

Most of the air in the low troposphere at the equatorial low-pressure belt in warm and moist. The reason for this is that this part of the Earth is getting constant high intensity solar radiation. That results in constantly high temperatures. The high temperatures result in warming up the land, as well as the water masses. The heat leads to lesser density of the air masses because the molecules are becoming more dispersed. The water has much higher rates of evaporation, and the water vapor leads to saturating the air with moist, as well as making it even less dense as the water vapor is lighter than the standard air mass. All of this results in less dense air masses that have lower air pressure, are warm, and have a lot of moisture in them.