Here's why:

* Electronegativity: Oxygen (O) has a higher electronegativity than chlorine (Cl). This means oxygen attracts electrons more strongly.

* Sharing Electrons: To achieve a stable electron configuration, both oxygen and chlorine need to gain electrons. They do this by sharing electrons, forming a covalent bond.

* Polar Covalent Bond: Since oxygen is more electronegative, the shared electrons spend more time closer to the oxygen atom. This creates a partial negative charge on the oxygen and a partial positive charge on the chlorine, resulting in a polar covalent bond.

Therefore, the bond between oxygen and chlorine is a polar covalent bond.