Which of the following pair is not isoelectronic species?
(At. no. Sm, 62; Er, 68: Yb, 70: Lu, 71; Eu, 63: Tb, 65; Tm, 69)

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${Yb}^{2} + and {Lu}^{3 +}$

${Eu}^{2 +} and {Tb}^{4 +}$

${Sm}^{2 +} and E u^{3 +}$

${Tb}^{2 +} and {Tm}^{4 +}$

answer is D.

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Detailed Solution

$\begin{array}{r} S m^{2 +} \to e l e c t r o n = 60 \\ E r^{3 +} \to e l e c t r o n = 65 \\ T b^{2 +} \to e l e c t r o n = 63 \\ T m^{4 +} \to e l e c t r o n = 65 \end{array}\} (n o t i s o e l e c t r o n i c)$

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