Between which altitudes does the greatest pressure change occur?

The greatest pressure change occurs between sea level and 18,000 feet due to the relationship between altitude and atmospheric pressure. As you ascend in altitude, the atmospheric pressure decreases significantly. At sea level, the standard atmospheric pressure is approximately 1013.25 hPa. As altitude increases, the pressure drops more rapidly within the lower layers of the atmosphere.

The most substantial rate of pressure change happens in the lower atmosphere, especially below about 18,000 feet. This is because the majority of the atmosphere's mass is concentrated closer to the Earth's surface, resulting in a steep gradient of pressure changes with altitude in this region. After reaching around 18,000 feet, the pressure decreases more gradually, leading to less drastic changes for the same elevations gained above that point.

Therefore, the correct choice highlights the critical altitude range where pilots and aviators must be particularly aware of pressure changes and their physiological effects, such as the potential onset of hypoxia. Understanding this dynamic is essential for safe flight operations.