MCQ
If the aufbau principle had not been foll owed. $Ca (Z = 20)$ would have been placed in the
  • A
    $s-block$
  • B
    $p-block$
  • $d-block$
  • D
    $f-block$

Answer

Correct option: C.
$d-block$
c
Electronic configuration of $Ca$ is $1 s ^2 \,2 s ^2\, 2 p ^6 \,3 s ^2\, 3 p ^6\, 4 s ^2$.

Filling of $3 d$ orbital starts after the filling of $4 s$ orbitals. If the Aufbau principle had not been followed, the filling of $3 d$ orbital would have been prior to filling of $4 s$ orbital and the electronic configuration of $Ca$ would have been $1 s ^2\, 2 s ^2 \,2 p ^6\, 3 s ^2\, 3 p ^6 \,3 d ^2$ and it would have been placed in the $d$-block.

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