JEE Main 2022 · 28 Jul · Shift 2 · Chemistry Q38

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ChemistrySingle correct+4 / -1Question 38 of 90

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)

\mathrm{Sm^{2+}}

and

\mathrm{Er^{3+}}

\mathrm{Yb^{2+}}

and

\mathrm{Lu^{3+}}

\mathrm{Eu^{2+}}

and

\mathrm{Tb^{4+}}

\mathrm{Tb^{2+}}

and

\mathrm{Tm^{4+}}

Answer and worked solution

Official answer: A

Electron counts. $\mathrm{Sm^{2+}}$ 60 vs $\mathrm{Er^{3+}}$ 65, not isoelectronic. $\mathrm{Tb^{2+}}$ 63 vs $\mathrm{Tm^{4+}}$ 65, not isoelectronic either. ( $\mathrm{Yb^{2+}}$ and $\mathrm{Lu^{3+}}$ both have 68; $\mathrm{Eu^{2+}}$ and $\mathrm{Tb^{4+}}$ both 61.)

NTA accepts (A) or (D). (A)

Topics:Lanthanoids

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JEE Main 2022 · 28 Jul · Shift 2, Chemistry question 38