Question

Why the small size of the cation leads to greater polarising power and why large charge on the cation leads to greater polarising power

Answer 1

Before we proceed to apply the concept of polarisation, let us define charge density as
charge density = charge on cation/ radius of cation
Smaller the cation greater is the electrostatic force with which its nucleus will attract electrons of the anion. Due to the smaller size of cation, the charge density on the cation is large due to which its polarising power is increased. Similarly, if the size of the anion is large, so it is easy to polarise an anion which is large in size.