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

Academic Chemistry NCERT Class 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.

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Updated on: 13-Mar-2023

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