Question

Why covalent character increases with oxidation state in d block elements?

Answer 1

On increasing oxidation state of a cation it's size decreases and hence its polarizing power increases.

Polarizing power = z/r where { z = charge on cation and r = radius}

According to Fajan's rule smaller is the size of cation greater will be its polarizing power and hence greater will be its covalent character. Therefore on increasing oxidation state covalent character increases and ionic character decreases.