What is the maximum covalency of oxygen ? Give examples.

Explanation

Oxygen usually forms two bonds. Its valency cannot be expanded due 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) O H^(+)` also has three bonds formed by oxygen.