1. Tardigrade
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  3. Chemistry
  4. Assertion: The 19th electron in potassium atom enters into the 4s - orbital and not into the 3d - orbital. Reason: (n + 1) rule is followed for determining the orbitals of the lowest energy state.

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Q. Assertion: The $19^{th}$ electron in potassium atom enters into the $4s$ - orbital and not into the $3d$ - orbital.
Reason: $(n + 1)$ rule is followed for determining the orbitals of the lowest energy state.

AIIMSAIIMS 1998Structure of Atom

Solution:

According to Aufbau principle, the unfilled shell with lowest $(n+ l)$ value will be filled first. Therefore, 4 s orbital is filled first then $3 d$ orbital.

for $4 s-$ orbital,$(n+ l)=4+0=4$

for $3 d -$ orbital,$(n+ l)=3+2=5$