MCQ
Krypton $(_{36}Kr)$ has the electronic configuration $[Ar]4s^2 ,3d^{10} ,4p^6 .$ The $37^{th}$ electron will go into which of following subshells
- A$4f$
- B$4d$
- C$3p$
- ✓$5s$
✓
Answer
Correct option: D.
$5s$
d
The $37^{th}$ electron will go into $5 s$ sub-level.
The $37^{th}$ electron will go into $5 s$ sub-level.
According to aufbau principle, the correct order of energy of $4 p$ and $5 s$-orbitals is $4 p \,<\,5 s$
Aufbau principle:
In the ground state of the atoms, the orbitals are filled with electrons in order of increasing energy.
The $4 p$ sub-energy level is at a lower energy than the $5$ sub-energy level
For $4 p , n =4$ and $1=1$. Hence, $( n +1)=4+1=5$
For $5 s , n =5$ and $1=0$. Hence, $( n +1)=5+0=5$
As the value of $( n +1)$ for $4 p$ orbital is same as that of $5 s$ orbital, $4 p$ orbital is filled before $5$ orbital as $4 p$ orbital has lower value of $n$ than $5 s$ orbital.
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