Q. Show the rate of decrease in atomic radius?

The rate of decrease in atomic radius along the lanthanide series and also along the actinide series is even less than that in the transition cries, since the  difference in the electronic configurations of these component is in the number of electrons in  the ante-penultimate (last but two) shell of electrons. But the additive effect of decrease in atomic radius across the fourteen elements of lanthanide series is quite substantial. This decrease in atomic radius across the lanthanide series is defined as lanthanide contraction.  Similarly, there is an actinide contraction across the actinide series. As a result of lanthanide contraction, the normal gain in size from Sc+Y+La disappears after the lanthanides.  And pairs of elements such as Hf and Zr, Nb and Ta, Mo and W, etc., possess nearly similar sizes. His properties of these elements, thus, are very similar. The similarities in properties within these pairs make their separation very difficult. Thus, due to lanthanide contraction the elements of 5d and 4d transition series resemble each other much more nearly than do the elements of 4d and 3d series.