Question

The 71st electron of an element X with an atomic number of 71 enters into the orbital 

(1) 6s 

(2) 6p 

(3) 5d 

(4) 4f

Answer 1

The correct option is (3) 5d.

Explanation:

₇₁Lu --> [Xe] 4f¹⁴ 5d¹ 6s² 

71th electron enters into 5d orbital 

so 5d is the orbital.

Comments

well that's the problem... the answer seems to be 4f somehow

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The electronic configuration of _70 Yb
_70 Yb = [Xe] 4f^14 5d^0 6s^2
That's why, Next element (i.e. _71 Lu) accommodate electron into 5d orbital. _71 Lu = [Xe] 4f^14 5d^1 6s^2
So, the 5d is the orbital.