Among the following the maximum covalent character is shown by the compound

Covalent character is favoured by Fajans' rule.(i) Larger the charge on the ions.(ii)Smaller the size of cations,(iii)Larger the size of anions(iv) Cation with 18-electron structure e.g.,  Cu+, then larger the polarizing power and the covalent character is favoured. In all the given compounds, anion is same Cl−, hence polarizing power is decided by size and charge of cation. Al3+ with maximum charge and smallest size has maximum polarizing power hence, AlCl3 has maximum covalent character.