What percentage of Earth's atmosphere is composed of water vapor?

The correct response indicates that water vapor comprises approximately 0.1% to 4% of Earth's atmosphere, which accurately reflects the variable nature of humidity levels in the atmosphere. Water vapor concentration can fluctuate greatly depending on various factors such as temperature, geographical location, and weather conditions. For example, in humid tropical regions, water vapor can reach levels closer to 4%, while in arid areas, it may be much lower.

While some options suggest higher or lower ranges, these do not align with the scientific understanding of atmospheric composition. The range provided in the correct choice encompasses typical values observed in various atmospheric conditions, thus making it the most accurate representation of water vapor concentrations in the Earth's atmosphere.