The gas in the air formed by the addition of an oxygen atom to a molecule is called ozone (O₃).

Here's how it forms:

* Oxygen (O₂) in the atmosphere is split by ultraviolet (UV) radiation from the sun. This creates individual oxygen atoms.

* These individual oxygen atoms then react with another oxygen molecule (O₂) to form ozone (O₃).

Ozone is a powerful oxidant and plays a vital role in the Earth's atmosphere by absorbing harmful UV radiation. However, high levels of ozone near the ground can be harmful to human health.