Question

For a multielectron system, which of the following will be the correct sequence of energy of orbitals?

• A. $3p<4s<4p<3d$
• B. $4s<3p<3d<4p$
• C. $3d<4s<4p<3p$
• D. $3p<4s<3d<4p$

Answer 1

The correct option is D $3p<4s<3d<4p$

As per Aufbau principle, energy of orbitals is calculated by the (n + l) rule.
Higher the value of $n+l$, higher will be the energy of the orbital.
Value of $n+l$ for 3p = 3 + 1 = 4
Value of $n+l$ for 4s = 4 + 0 = 4
Value of $n+l$ for 4p = 4 + 1 = 5
Value of $n+l$ for 3d = 3 + 2 = 5
When the value of $n+l$ is same for two orbitals, then lower the value of n, lower be the energy.
So, the order becomes 3p < 4s <3d < 4p.