Question

The correct order of decreasing polarisability of anion is

Answer 1

Polarization means  the outer most shell of anion  disturbs by cation due to its attraction towards the other electrons. Amount of deformation done to the outermost shell is called the polarizability of anion. Note that more the polarizability, more covalent bond in the compound.

The  order of polarizability of anions containg following type:

I> Br> Cl> F

Answer 2

The ability of an anion to get polarised is called polarisibilty of an anion.

The ability of a cation to polarise an anion is termed as polarising power of the cation.

Larger the size of anion/smaller the size of cation, greater is the polarising power .

Hence the order for halide ions goes like this ..

I- > Br- > Cl- > F-