What is the chemical formula of water?

The story behind the answer

The correct formula for water is H2O—two hydrogen atoms bonded to one oxygen atom (O is the letter O for oxygen, not the numeral 0). These are polar covalent bonds, giving the molecule a bent shape and partial charges that explain water’s high cohesion, surface tension, and remarkable ability to dissolve many substances.

The other options are different substances: H2O2 is hydrogen peroxide (a disinfectant/bleach), HO2 is the reactive hydroperoxyl radical, and H2 is molecular hydrogen gas.