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 state and as part of various compounds. It makes up about 46% of the Earth's crust in the form of minerals like silicates and oxides. In the atmosphere, oxygen exists primarily as O2 gas, making it essential for life as it supports respiration in aerobic organisms. Additionally, oxygen plays a crucial role in water's composition (H2O), which is fundamental to all known forms of life, and it is highly reactive, readily forming compounds with a wide variety of elements. This high reactivity is key to its abundance in nature, as it easily combines with other elements to form stable compounds. Consequently, oxygen's presence in both free and combined states establishes it as the most abundant element on the planet.