What is the main characteristic of air in a low pressure zone?

In a low pressure zone, the main characteristic of air is that it rises and expands. This is due to the fact that in a low pressure area, the surrounding atmospheric pressure is higher, which pushes the air upwards. As the air rises, it encounters lower atmospheric pressure at higher altitudes, causing it to expand.

This process results in cooling, as a warm air parcel rises, it expands due to the decreasing pressure. The cooling of the air can lead to condensation and cloud formation, which are significant features often associated with low pressure systems. Such systems are typically linked to unsettled weather and precipitation.

The other choices describe different behaviors of air that are not characteristic of low pressure zones. For instance, air warming as it sinks would pertain to high pressure zones, where descending air compresses and warms up. Static air implies no movement, which contrasts with the dynamic nature of low pressure areas where air is actively rising and causing changes in weather patterns.