Which inorganic compound is most abundant on Earth?

Water is the most abundant inorganic compound on Earth, making up about 71% of the planet's surface. It exists in various forms—liquid, solid (ice), and gas (water vapor)—and plays a critical role in supporting all known forms of life. Water is essential for numerous biological processes, including cellular functions, temperature regulation, and nutrient transport. Its unique chemical properties, such as being a solvent for many substances and its high specific heat capacity, also contribute significantly to Earth's climate and ecosystems.

While carbon dioxide, oxygen, and ammonia are important inorganic compounds, their abundance in comparison to water is much lower. Carbon dioxide is primarily found in the atmosphere and in dissolved forms in oceans; oxygen, although vital for respiration and combustion, is less abundant as a compound when considering the overall volume of substances present on Earth. Ammonia, while important in biological processes and as a nutrient, is not nearly as abundant in terms of total quantity when compared to water.