MCQ practice · SSC Chemistry Board questions · Chapter 3: Structure of Matter
How many electrons are in the last shell of the metal ion of salt A?
Think it through first, then pick an option.
- a 16
- b 17
- c 18
- d 19
Answer and explanation
Correct answer: b 17
Right. Cu + conc. H₂SO₄ → CuSO₄ (A) + SO₂ + H₂O. Cu²⁺ has 27 electrons: 4s¹ and one 3d have gone, leaving ...3s² 3p⁶ 3d⁹. The last shell, M, holds 2 + 6 + 9 = 17.
Why the other options are wrong
- a 16: 16 would need one more 3d electron removed (Cu³⁺); here A is CuSO₄ and the ion is Cu²⁺.
- c 18: 18 is the M shell of the Cu atom (or Cu⁺), 3d¹⁰; Cu²⁺ loses one more 3d electron, so 17.
- d 19: The M shell cannot hold more than 18, and Cu²⁺ has 17 in it.
More board questions on this topic
- How many electrons are in the M shell of ₂₅Mn²⁺?
- The electronic configuration 1s²2s²2p⁶3s²3p⁶ is seen in −
- Which element follows the (n − 1)d¹⁰ ns¹ configuration?
- Which orbital has comparatively lower energy?
Your account is open, so all 30,000+ MCQs from every chapter are yours. Start practising SSC Chemistry →
Want to keep going?
A free account carries you on to the next questions and opens 30,000+ MCQs from every chapter. Join before launch and Chirkut bundles are 60% off.
The ones you missed, worth one more look