The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belong to the same group?
  1. A and B
  2. B and D
  3. A and C
  4. D and E

AcademicChemistryNCERTClass 10

Correct answer: (c) A and C 

Explanation: Electronic configuration of A (9) : 2  7

Electronic configuration of C (17): 2  8 7

Group number of A and B = no. of valence electrons + 10

                                           =  7+10 = 17.

raja
Updated on 10-Oct-2022 13:19:20

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