Because of lanthnoid contractoin, which of the following pairs of elements have nearly same atomic radii ? (Number in the parentrhesis are atomic numbers)

Options

A. `Zr (40)` and `Ta (73)`
B. `Ti (22)` and `Zr (40)`
C. `Zr (40` and `Nb (41)`
D. `Zr (40)` and `Hf (72)`

Answer

D

Explanation

As a result of lanthanoid contraction the normal increase in size form `Sc rarr Y rarr La` disapperas after the lanthanoids, and thus pairs of elements such as Zr and Hf (Group 4), Nb and Ta (Group 5), Mo and W (Group 6), etc., possess nearly similar sizes. Consequently, the properties of these elements are very similar. The similarites in properties make their separtion very difficult.