Which of the following lanthanoid elements exhibits $+2$ and $+3$ oxidation states?

The correct statements among the following are:
$A$. $Mo(VI)$ and $W(VI)$ are less stable than $Cr(VI)$.
$B$. $Ce^{4+}$ and $Tb^{4+}$ are oxidants, while $Eu^{2+}$ and $Yb^{2+}$ are reductants.
$C$. $Cm$ and $Am$ have seven unpaired electrons.
$D$. Actinoid contraction is greater from element to element than lanthanoid contraction.
Choose the correct answer from the options given below:

Determine the correct $(T)$ and incorrect $(F)$ statements from the following:
$(a)$ Mischmetal contains lanthanoids and iron.
$(b)$ The symbol for Cerium is $Cs$.
$(c)$ The symbol for Cerium is $Ce$.

Which among the following properties of lanthanoids is $NOT$ true?

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

Identify the formula of compound $(B)$ formed in the following reaction:
$(i)$ Lanthanoids $(Ln)$ are burnt in oxygen to form compound $(A)$.
$(ii)$ Compound $(A)$ reacts with $CO_2$ in excess to form compound $(B)$.