Can chlorine have an expanded octet?

Yes, chlorine can have an expanded octet because it has empty $3d$ orbitals available that can accommodate more than eight electrons. As a Period 3 element, chlorine has access to $3s,$ $3p,$ and $3d$ orbitals, which allows it to form compounds where it is surrounded by more than eight electrons. Common examples include $\ce{ClF3}$ (chlorine trifluoride) where chlorine has 10 electrons around it, and $\ce{ClF5}$ (chlorine pentafluoride) where chlorine has 12 electrons. This ability to expand the octet is only possible for elements in Period 3 and beyond because they have $d$ orbitals available in their valence shell.