what is h2o ?

Water (H2O, HOH) is the most abundant molecule on Earth's surface, composing of about 70% of the Earth's surface in liquid, solid, and gaseous states. (Note that the earth's surface is usually considered to be the volume between 2 concentric spheres of some thickness, like 1.0 km. Water in clouds is mostly solid and liquid. Water in atmosphere outside of clouds is mostly vapor. Water in the ground also exists in all 3 forms). It is in dynamic equilibrium between the liquid and gas states at standard temperature and pressure. At room temperature, it is a nearly colorless (with a hint of blue), tasteless, and odorless liquid. Many substances dissolve in water and it is commonly referred to as the universal solvent. Because of this, water in nature and in use is rarely pure, and may have some properties different from those in the laboratory. However, there are many compounds that are essentially, if not completely, insoluble in water. Water is the only common substance found naturally in all three common states of matter—for other substances, see Chemical properties. Water is essential for all life on Earth. Water also usually makes up 55% to 78% of the human body.[3]