A Cl-Cl bond is a nonpolar covalent bond. This is because both chlorine atoms have the same electronegativity, meaning they share the electrons equally. In a covalent bond, atoms share electrons to achieve a full outer shell. When the atoms involved are identical, as in the case of two chlorine atoms, the bond is nonpolar because there is no difference in electronegativity to cause a dipole moment.
In contrast, an ionic bond forms when there is a significant difference in electronegativity between two atoms, leading to the transfer of electrons from one atom to another. A polar covalent bond occurs when there is a moderate difference in electronegativity, causing an uneven sharing of electrons. Since both chlorine atoms in a Cl-Cl bond are identical, neither of these conditions is met, making the bond nonpolar covalent.