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NDA 2016 GAT · General Knowledge · Atomic Structure, Periodic Table and Bonding · medium

An element with electronic configuration 2, 8, 7 belongs to

Single correct option

An element with electronic configuration 2, 8, 7 belongs to
  1. A. Group 17 and Period 3
  2. B. Group 7 and Period 2
  3. C. Group 17 and Period 2
  4. D. Group 15 and Period 3
Show answer and solution

Answer: (A) Group 17 and Period 3

Three shells are occupied, so the element is in Period 3. Seven valence electrons place it in Group 17, the halogens (modern numbering, 10 + 7). The element is chlorine, atomic number 17. Group 7 is an older notation for a different block, and Period 2 would need only two shells.
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Original question written in the NDA 2016 GAT pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake