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

NEETprep Answer: Separation of Zr and Hf are quite difficult because of janthanoid contraction. Due to lanthanoid contraction, they have almost same size (Zr = 460 pmand Hf = 159 pr) and thus, similar chemical properties. That's whyit is very difficult to separate them by chemical methods.