Gaseous hydrogen burns in the presence of oxygen to form water: #2H_2 + O_2 -> 2H_2O + en ergy#. Which molecule is oxidized and what kind of bond is formed?
Clearly, elemental hydrogen is oxidized.........
Given this formalism, because the oxidation number of hydrogen has manifestly increased, elemental hydrogen is said to be OXIDIZED. And likewise, because the oxidation number of elemental oxygen has decreased, oxygen is said to be REDUCED.
We can imagine that each hydrogen atom has donated an electron to the oxygen atom, thereby oxidizing the hydrogen atoms, and reducing the oxygen.
The hydroxyl bonds in water are clearly covalent bonds........