Question

# According to the Aufbau Principle, the correct order of energy of 3d, 4s and 4p orbitals is:

A

3d<4s<4p

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B

4s<3d<4p

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C

4s<4p<3d

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D

4p< 3d<4s

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Solution

## The correct option is B 4s<3d<4pThe 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)=5For 3d orbital, l=2 and n=3 and (n+l)=5For 4s orbital, l=0 and n=4 and (n+l)=4For 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).

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