What is lanthanoid contraction? What are the consequences of lanthanold contraction?

Explanation

Lanthoanoid contraction : The regular decrease in the atomic and ionic radii of lanthanoids with increasing atomic number is known as Lanthaanoid contraction.
Consequences of Lanthanoid contraction :
(i) Diffcult to separate the lanthanoids because the change in ionic radii is very small, their chemical properties are similar. Hence, separation of lanthanoids are difficult.
(ii) Similarity in size of elements belonging to same group of second and third transition series due to lanthanoid contraction the size of Zr (160 pm) is same as that of `H_(f)(159).`