Which of the following lanthanoids have $[Xe] 4f^x 5d^1 6s^2$ configuration in their ground state? $(x = 1-14)$

Assertion : Europium $(II)$ is more stable than cerium $(II)$.
Reason : Cerium salts are used as catalyst in petroleum cracking.

Which of the following pairs show $+2$ oxidation state?

What is the general formula of lanthanoid hydroxide? (Consider $Ln$ as any lanthanoid element)

Which actinoid elements have a $5f^{14}$ electronic configuration in their atoms?

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.