MCQ practice · SSC Chemistry Board questions · Chapter 3: Structure of Matter
How many electrons are in the last sublevel of the element's configuration?
Think it through first, then pick an option.
- a 4
- b 3
- c 2
- d 1
Answer and explanation
Correct answer: d 1
Z = 29 is Cu: ...3d¹⁰ 4s¹, so the last sublevel has 1.
Why the other options are wrong
- a 4: 4 matches no sublevel here; ₂₉X is Cu, whose last sublevel is 4s¹.
- b 3: Three fits no sublevel of copper; Cu ends in 4s¹.
- c 2: The simple rule would give 4s², but copper shifts one electron into 3d.
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