It is difficult to find lanthanides in their purest form. Explain.

Explanation

The chemical properties of the lanthanides are very similar because : 1. most of the elements form compounds in the + 3 oxidation state and 2. there is not much difference in the ionic radii of the `Ln^(3+)` ions. Due to such striking similarities in their chemical properties, the elements cannot be separated from one another and hence, cannot be obtained in the purest form.