What is the maximum covalency of oxygen ? Give examples.

Explanation

Oxygen usually forms two bonds. Its valency cannot be expanded due to lack to lack of valence d - orbitals. However, the maximum covalency of oxygen is three, due to an additional dative bond formed by oxygen using one of its lone pairs.
Hydronium ion, `H_(3)O^(+)` has two covalent bonds and one coordinate covalent bond formed by oxygen atom. Oxonium ion, `(C_(2)H_(5))_(2)OH^(+)` also has three bonds formed by oxygen.