Which of the following is ionic

As the size of anion increases,polarisability of anion increases,hence distortion of electron cloud in anion increases,sharing proprty of electron cloud in M—X bond increases,∴ Covalent character increases,hence Ionic character decreases.% of ionic character:→AlF3>AlCl3>AlBr3>AlI3Covalent chracter ∝1Ionic character Polarisability: The ability of a anion to undergo distortion by cation is called polarisability of anion.