What largely determines the amount of water vapor that air can hold?

The correct answer is based on the concept of how air temperature affects the capacity of air to hold moisture. Warmer air can hold more water vapor than cooler air. This is due to the increased kinetic energy of the molecules in warmer conditions, which allows more water molecules to remain in gaseous form rather than condensing into liquid water.

As temperature rises, the saturation vapor pressure increases, meaning that a higher amount of moisture can be contained before reaching the point of saturation or condensation. Conversely, cooler air has a lower capacity for moisture, and this relationship is critical in meteorology, especially when understanding weather patterns, cloud formation, and precipitation.

While air pressure, humidity, and altitude can influence various aspects of weather and air quality, they do not primarily determine the water-holding capacity of air as fundamentally as temperature does.