Although Zr belongs to 4d and Hf belongs to 5d transition series, but it is quite difficult to separate them. Why?

Zirconium (Zr) belongs to. ‘4d and Hafnium (Hf) belongs to 5d transition series: It is difficult to separate them. Explain.

Which one belongs to 3d-transition series

Which does not belong to first transition series?

Although Zirconium belongs to 4d-transition series and Hafnium belongs to 5d transition series , even then they show similar physical and chemical properties because _______ .

Which of the following group belongs to transition series ?