Concept: The order of orbital filling is strictly determined by the Aufbau principle, which uses the \( (n+l) \) rule to rank energy levels.
Formula: $$ \text{Energy} \propto (n+l) $$
Solution: - The \( 6d \) orbital has \( n=6 \) and \( l=2 \). Its \( (n+l) \) sum is \( 6 + 2 = 8 \).
- After \( 6d \), the next orbital must either have a higher \( (n+l) \) sum, or the same sum but a higher principal quantum number \( n \).
- Let's test \( 7p \): \( n=7, l=1 \implies n+l = 7 + 1 = 8 \).
- Since both \( 6d \) and \( 7p \) have a sum of 8, the orbital with the higher \( n \) is filled next. Thus, \( 7p \) follows \( 6d \).
Why other options are incorrect: \( 7s \) is filled much earlier (\( n+l = 7 \)). \( 7d \) and \( 7f \) have much higher energy levels and follow later in the sequence.
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