Question

The polarising ability of which one of the following is the highest
1 small highly+Ve ion
2 large +Ve ion
3 small highly -Ve ion
4 large -Ve ion

Answer 1

For cations with the same radius, the higher the charge is, the larger the polarizing power is. For cations with the same charge, the smaller the radius is, the larger the polarizing power is.

Small cation: the high polarizing power stems from the greater concentration of positive charge on a small area. This explains why LiBr is more covalent than KBr (Li⁺ 90 pm cf. K⁺ 152 pm).

Large anion: the high polarizability stems from the larger size where the outer electrons are more loosely held and can be more easily distorted by the cation. This explains why for the common halides, iodides, are the most covalent in nature (I^- 206 pm).

The answer for the above question depends on the element