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Electrons are identified by their quantum numbers n and l as follows: (i) n = 4, l = 1 (ii) n = 4, l = 0 (iii) n = 3, l = 2 (iv) n = 3, l = 1 Arrange these electrons in increasing order of energy (lowest to highest).

1. (iv) < (ii) < (iii) < (i)
2. (iii) < (ii) < (iv) < (i)
3. (i) < (iii) < (ii) < (iv)
4. (iii) < (i) < (iv) < (ii)

Correct answer: (iv) < (ii) < (iii) < (i)

Solution

The (n + l) rule gives: (ii) and (iv) both have n+l=4, with (iv) having n=3 < n=4, so (iv) < (ii). Similarly (iii) and (i) both have n+l=5, with (iii) having n=3 < n=4, so (iii) < (i). Combined order: (iv) < (ii) < (iii) < (i).

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