Which of the following gases is noted for having variations in volume at altitudes up to 80km?

Ozone is a gas that exhibits significant variations in volume, particularly in the stratosphere, which extends from about 10 km to around 50 km above sea level. Its concentration fluctuates based on factors such as solar radiation, temperature, and chemical interactions. Ozone is produced through photodissociation of oxygen molecules by ultraviolet radiation, resulting in a dynamic equilibrium that can change with altitude and regional atmospheric conditions.

The presence of ozone is essential for absorbing harmful ultraviolet radiation from the sun, which further influences its distribution and volume at different altitudes. The variability of ozone levels at elevations leading up to 80 km is a well-studied phenomenon, making it the only gas among the options that demonstrate such pronounced divergence in volume with altitude.

In contrast, nitrogen and argon make up a significant portion of the atmosphere but show little variation in concentration with altitude due to their inert nature and how they are distributed throughout the atmosphere. Helium, though present, is a trace gas and does not vary in volume to a significant extent in the atmosphere compared to ozone. Thus, the behavior of ozone in the atmosphere is key to understanding its role and the variations noted in the specified altitude range.