(પરમાણુ ક્રમાંક $Sm , 62 ; Er , 68: Yb , 70: Lu , 71 ; Eu , 63: Tb$, $65$; $\operatorname{Tm}, 69)$
\(Er ^{3+} \rightarrow\) electron \(=65\)
\(Tb ^{2+} \rightarrow\) electron \(=63\)
\(Tm ^{4+} \rightarrow\) electron \(=65\)
all are \((not\,isoelectronic)\)