question_answer 82)

    The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and13 respectively. Which pair of elements belong to the same group? (a) A and B                          (b) B and D                          (c) A and C                          (d) D and E

Answer:

                  (c) Electronic configuration of A (atomic number 9) is 2, 7. Electronic configuration of B (atomic number11) is 2, 8, 1. Electronic configuration of C (atomic number 17) is 2, 8, 7 Electronic configuration of D (atomic number 12) is 2, 8, 2. Electronic configuration off (atomic number 13) is 2, 8, 3. Elements which differ in atomic number by 8 i.e., 9 (A fluorine) and 17 (Cl, chlorine) lie in the same group i.e., group 17 (halogens).