Covalent character is favoured by Fajan's 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 polarising power and the covalent character is favoured.In all the given compounds, anion is same (Cl−), hence polarising power is decided by size and charge of cation.Al3+ with maximum charge and smallest size has maximum polarising power hence, AlCl3​ is maximum covalent.