Which lanthanoid element 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:

Which of the following elements belongs to the actinoids?

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

Which of the following elements belongs to the actinide series?

Which of the following lanthanoids exhibits no effective magnetic moment in the $+3$ oxidation state?