Which of the following components of air varies significantly in concentration from place to place?

Water vapor is the component of air that varies significantly in concentration from place to place. This variability is primarily due to factors such as temperature, humidity, and geographical location. For example, areas near large bodies of water or in tropical regions tend to have higher concentrations of water vapor, while arid zones or regions experiencing cold weather will have much lower concentrations.

Unlike water vapor, nitrogen and argon are relatively stable and consistently make up a large portion of the atmosphere regardless of location. Carbon dioxide does fluctuate, particularly due to human activities and seasonal changes, but its overall atmospheric concentration does not vary to the same extent as water vapor, which can change rapidly based on local environmental conditions. Thus, water vapor's concentration is highly dynamic, making it the correct choice in this context.