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?- A and B
- B and D
- A and C
- D and E
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.
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