The elements A, B, C, D and E have atomic numbers 9, 11, 17, 12 and 13 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.
(c). Elements A (Z = 9) and C (Z = 17) belong to the same group. It is a halogen family (group 17).