Chemistry - Atomic Structure Question with Solution | TestHub

Based on the $(n+l)$ rule, orbital energy increases as the sum of the principal ($n$) and azimuthal ($l$) quantum numbers increases; if sums are equal, the higher $n$ value takes priority.

Option (B) is correct: $3p$$(3+1=4)$ is lower in energy than $4s$$(4+0=4)$ because it has a lower $n$ value.

Option (C) is correct: $3d$$(3+2=5)$ has a higher $(n+l)$ sum than $4s$$(4+0=4)$, placing it higher in energy.

Options (A) and (D) are incorrect because $4f$$(7)$ is greater than $3d$$(5)$, and $5s$$(5,n=5)$ is greater than $4p$$(5,n=4)$.