What is the most common form of oxygen found in the atmosphere?

Molecular oxygen is indeed the most common form of oxygen found in the atmosphere. It exists as O2, meaning each molecule is composed of two oxygen atoms. This form accounts for approximately 21% of the Earth's atmosphere and is essential for the respiratory processes of most living organisms, as it is what they utilize for cellular respiration.

Atomic oxygen, on the other hand, exists as single oxygen atoms and is much less common in the atmosphere due to its high reactivity; it quickly combines with other atoms or molecules. Ozone, which consists of three oxygen atoms (O3), is present in smaller quantities and primarily found in the stratosphere, where it plays a critical role in absorbing ultraviolet radiation. Hydrogen peroxide is not a naturally occurring form of oxygen in the atmosphere; it is a chemical compound (H2O2) that can be found in trace amounts under specific conditions but is not a significant or common atmospheric component.