What element is crucial in the formation of ozone in the upper atmosphere?

The formation of ozone in the upper atmosphere primarily occurs through a process that involves ultra-violet light. When ultraviolet (UV) radiation from the sun reaches the Earth's stratosphere, it provides the energy needed to break apart oxygen molecules (O₂) into individual oxygen atoms. These free oxygen atoms can then react with other oxygen molecules to form ozone (O₃).

This reaction is essential for creating the ozone layer, which plays a protective role by absorbing a significant portion of the sun's harmful UV radiation. Without the influence of UV light, the formation of ozone would not take place in the atmosphere, highlighting its crucial role in this chemical process.

In contrast, other options such as nitrogen, carbon dioxide, and hydrogen do not play a direct role in the formation of ozone in the same way that ultra-violet light does. Therefore, understanding the role of UV light is key to comprehending ozone chemistry and its implications for atmospheric science.