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

(c) : We know that, extent of polarisation ∝ covalent character in ionic bond. 

Fajan’s rule states that 

(i) the polarising power of cation increases, with increase in magnitude of positive charge on the cation 

Therefore, polarising power ∝ charge of cation 

(ii) the polarising power of cation increases with the decrease in the size of a cation. 

Therefore, polarising power ∝ 1/(size of cation) 

Here the AlCl₃ is satisfying the above two conditions i.e., Al is in +3 oxidation state and also has small size. So it has more covalent character.