Hint: As we know that covalency tells the number of electrons contributed by an atom for sharing of electrons with other same or different while mutually sharing a covalent bond. So here we have to tell the maximum covalency of chlorine atoms i.e., maximum number of bonds it can possibly make with other atoms or groups.
Complete answer: Let us first begin with the discussion of chlorine element and covalency followed by calculating its maximum covalency as follows:- -Chlorine: It is a chemical element denoted by symbol ‘Cl’ and has atomic number 17. It belongs to the halogen family that is group-17 and is the second-lightest of all the halogens available. Its properties are mostly intermediate between fluorine (F) and bromine (Br) elements. Also it is a yellow-green gas at standard temperature and pressure conditions. -Since it belongs to the halogen group, it has 7 electrons in its valence shell like all the other halogen elements. Also its valency is -1. -Covalency: It is the number of electrons contributed by an atom for sharing of electrons with another same or different while mutually sharing a covalent bond. -Maximum covalency is the maximum number of covalent bonds that an atom can form with other atoms. An atom can show maximum covalency up to its group number (especially for elements that have d-orbitals). For example: maximum covalency of sulphur is 6. -Since chlorine has empty d-orbitals, its valence electrons can jump to excited state and become unpaired for bonding purpose. Total number of valence electrons of chlorine is 7, so its maximum covalency is also 7. -Hence, the maximum covalency of chlorine is 7.
Note: -Remember that second period elements have maximum covalency equal to their actual unpaired electrons without any involvement of excitation because they are small in size and do not have empty d-orbitals to jump electrons to excited state.