JEE MAIN - Chemistry (2022 - 28th July Evening Shift - No. 3)
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 $$\mathrm{Tm}^{4+}$$
Explanation
Species having same number of electrons are isoelectronic
$\left.\begin{array}{l}\mathrm{Tb} \longrightarrow 65 \mathrm{~Tb}^{+2} \longrightarrow 63 \text { electrons } \\ \mathrm{Tm} \longrightarrow 69 ~\mathrm{Tm}^{+4} \longrightarrow 65 \text { electrons }\end{array}\right\}$ not isoelectronic
$\left.\begin{array}{c}\mathrm{Sm}^{+2} \longrightarrow 60 \text { electrons } \\ \mathrm{Er}^{+3} \longrightarrow 65 \text { electrons }\end{array}\right\}$ not isoelectronic
$\left.\begin{array}{l}\mathrm{Tb} \longrightarrow 65 \mathrm{~Tb}^{+2} \longrightarrow 63 \text { electrons } \\ \mathrm{Tm} \longrightarrow 69 ~\mathrm{Tm}^{+4} \longrightarrow 65 \text { electrons }\end{array}\right\}$ not isoelectronic
$\left.\begin{array}{c}\mathrm{Sm}^{+2} \longrightarrow 60 \text { electrons } \\ \mathrm{Er}^{+3} \longrightarrow 65 \text { electrons }\end{array}\right\}$ not isoelectronic
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