Question

Why do electrons enter the 4s orbital before entering the 3d orbital

Answer 1

the moiller's diagram 4s has 2 electrons 3d has 10 electrons

Answer 2

heya your answer
This is due to Aufbau principle& molar chart.
According to Aufbau principle In the ground state the electronic configuration can be built up by placing electrons in the lowest available orbitals and the total number of electrons had a is equal to the atomic number.
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