Transition and InnerTransition Elements - Result Question 11
11. The $7 \mathrm{I}^{\mathrm{st}}$ electron of an element $X$ with an atomic number of 71 enters into the orbital
(2019 Main, 10 Jan II)
(a) $4 f$
(b) $6 p$
(c) $5 d$
(d) $6 s$
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Answer:
Correct Answer: 11. (c)
Solution: In the lanthanoid series, atomic number of fourteen $4 f$-block elements ranges from $58(\mathrm{Ce})$ to $71(\mathrm{Lu})$. Ytterbium, $\mathrm{Yb}(Z=70)$ has electronic configuration : $[\mathrm{Xe}] 4 f^{14} 6 s^2$. So, the 71 nth electron of lutetium, $\mathrm{Lu}(Z=71)$ should enter into $5 d$ orbital and its (here, Lu is ’ $X$ ‘) electronic configuration will be : $[\mathrm{Xe}] 4 f^{14} 5 d^1 6 s^2$. It happens so, because $f$-block elements have general electronic configuration, $(n-2) f^{1-14}(n-1) d^{1-10} n s^2$. Therefore, option (c) is correct.
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