What does the environmental lapse rate describe?

The environmental lapse rate describes the actual temperature decline with height in the atmosphere. This concept is crucial in meteorology and is defined as the rate at which air temperature decreases with an increase in altitude. Generally, in the troposphere, temperature typically decreases about 6.5 degrees Celsius for every kilometer (or about 3.6 degrees Fahrenheit per 1,000 feet) of elevation gain. Understanding the environmental lapse rate helps meteorologists predict weather patterns and atmospheric stability.

The other choices do not accurately describe this concept. Temperature stability refers to whether air remains at a constant temperature or is subject to variations; air pressure changes address how pressure alters with elevation, which is a different aspect of atmospheric science; humidity variations focus on the moisture content of the air rather than how temperature changes with height.