Question

The second and third rows of transition elements resemble each other much more than they resemble the first row. Explain why?

Answer 1

The atomic size or atomic radii of second and third row transition elements are almost comparable due to the lanthanoid contraction whereas the difference in atomic radii of first and second or first and third row is large. As a result, second and third rows of transition elements have almost similar physical and chemical properties.

$\text{Additional Information}$
Lanthanoid contraction is the overall decrease in size (atomic and ionic radii) of ions and atoms of the lanthanoid series with the increasing atomic number from $La$ to $Lu$.