Transition and InnerTransition Elements - Result Question 10
####11. The $71^{\text {st }}$ 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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Solution:
- In the lanthanoid series, atomic number of fourteen $4 f$-block elements ranges from $58(Ce)$ to $71(Lu)$.
Ytterbium, $Yb(Z=70)$ has electronic configuration : $[Xe] 4 f^{14} 6 s^{2}$. So, the 71 nth electron of lutetium, $Lu(Z=71)$ should enter into $5 d$ orbital and its (here, $Lu$ is ’ $X$ ‘) electronic configuration will be : $[Xe] 4 f^{14} 5 d^{1} 6 s^{2}$. 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.
