Identify all the correct statements for Lanthanide contraction. (A) The covalent properties of the Lanthanide metal hydroxides increases from $\mathrm{La}$ to $\mathrm{Lu}$. (B) The chemical reactivity decreases from $\mathrm{La}$ to $\mathrm{Lu}$. (C) $\mathrm{La}(\mathrm{OH})_3$ is more basic than $\mathrm{Lu}(\mathrm{OH})_3$ (D) Zr and Hf have about the same radius. (E) Separation of Lanthanides from one another is easy

The change in ionic radii is Lanthanide series is very small, their chemical properties are small. Thus, the separation of Lanthanide is difficult due to consequence of Lanthanide contraction. The ionic radii of same positive charge of $\mathrm{La}$ to $\mathrm{Lu}$ decreases. So, the polarizing power towards hydroxyl group increases. Therefore the covalent character increases. Thus, $\mathrm{La}(\mathrm{OH})_3$ is more basic than $\mathrm{Lu}(\mathrm{OH})_3$. $\mathrm{Zr}$ and $\mathrm{Hf}$ have the almost same radius as the electrons in the elements after $\mathrm{Zr}$ are added into the deep seated $4 \mathrm{f}$ orbitals which do not take part in the chemical reaction.