Question

Why are the size of 4d and 5d trancition elements almost same?

Answer 1

Answer:

The size of one group of 5d and 4d transition series is almost same. In group 3 elements, there is regular increase in size from Sc to Y and from Y to La. But after this the size of one group in 4d to 5d series is almost same because lanthanoids come in between them: and size decreases due to lanthanoid contraction.