According to the Aufbau Principle, the correct order of energy of 3d, 4s and 4p orbitals is:
The explanation for the correct option:
According to the Aufbau principle, in the ground state of the atoms, the orbitals are filled with electrons to increase energy.
(B) 4s<3d<4p: The increasing order of energy of orbitals can find out by the (n+l) rule.
For 4p orbital, l=1 and n=4 and (n+l)=5
For 3d orbital, l=2 and n=3 and (n+l)=5
For 4s orbital, l=0 and n=4 and (n+l)=4
For the same value of (n+l), we can choose the higher value of n which will be having higher energy.
Therefore, the correct order of energy of 3d, 4s and 4p-orbitals is 4s<3d<4p.
The explanation for the incorrect option:
(A) 3d<4s<4p: Since the (n+l) value of 3d is greater than 4s, the option is wrong.
(C) 4s<4p<3d: The (n+l) value of 4p is greater than 3d.So the option is wrong.
(D) 4p< 3d<4s: The (n+l) value of 4p is greater than 3d and 4s.So the option is wrong.
Therefore, the correct option is (B).