MCQ practice · SSC Chemistry Board questions · Chapter 3: Structure of Matter
Which one will electrons enter first?
Think it through first, then pick an option.
- a 5s
- b 5d
- c 4p
- d 4f
Answer and explanation
Correct answer: c 4p
4p has the lowest n + l (5), and it beats 5s on the smaller n.
Why the other options are wrong
- a 5s: 5s has n + l = 5, the same as 4p, but a larger n; so 4p comes first.
- b 5d: 5d has n + l = 7, which is higher, so it fills later than 4p.
- d 4f: 4f has n + l = 7; 4p, with 5, fills well before it.
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