The most common lanthanide is

Which one of the following ions exhibits paramagnetic property?

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

The outer electronic structure of lawrencium (atomic number $103$) is

Which of the following compounds is used in gas lighters?

The first element of the rare-earth metals is: