Why is the separation of lanthanide elements difficult?

Why is the separation of lanthanoid elements difficult?

Why is separation of lanthanide elements difficult ?

Why separation of lanthanoid elements is difficult ?

Separation of lanthanoid elements is difficult. Why ?

(a) Separation of lanthanide elements is difficult. Explain. (b) Sm^(2+), Eu^(2+) and Yb^(2+) ions in solutions are good reducing agents but an aqueous solution of Ce^(4+) is a good oxidising agent. Why?

Which is the non-lanthanide element ?

Which is the non-lanthanide element ?