In general , the configuration of lanthanides in `(n-2) f^(1-14) (n-1) s^(2) p^(6) d^(0-1) ns^(2)` . It has been observed that , with increase in atomic number of lanthanides , there is a gradual decrease in ionic radii from La `(1.22 A^(@))` to `Lu(0.99 A^(@))` . The reason for decrease in ionic radii is an increase in