Which one of the lanthanoids given below is the most stable in divalent form?
\( \mathrm{Ce} \) (Atomic Number \( 58 \))
\( \mathrm{Sm} \) (Atomic Number \( 62 \))
\( \mathrm{Eu} \) (Atomic Number \( 63 \))
\( \mathrm{Yb} \) (Atomic Number \( 70 \))