What is the most abundant element found on Earth, both free and in compounds?

Oxygen is the most abundant element found on Earth, both in its free form and as a part of various compounds. It constitutes a significant portion of the Earth's crust, primarily found in minerals and water. In the atmosphere, oxygen exists as a diatomic molecule (O2) and plays a crucial role in respiration for living organisms as well as in combustion reactions.

In the Earth's crust, oxygen is primarily combined with silicon to form silicate minerals, which are the predominant group of minerals in the Earth's lithosphere. Together with other elements, oxygen makes up about 47% of the Earth's crust by weight. Additionally, oxygen is a key element in water (H2O), which covers about 71% of the Earth's surface. This immense presence in both free and combined forms highlights its abundance compared to the other elements listed.

Hydrogen, while the most abundant element in the universe, is not as prevalent on Earth in its elemental state. Nitrogen, important for biological processes, is predominant in the atmosphere but less so on the Earth’s surface compared to oxygen. Carbon, while crucial for life and prevalent in organic compounds, is not as abundant in the Earth's crust or atmosphere as oxygen. Thus, oxygen clearly stands out as the most abundant