Question

The atomic number of elements A, B and C are (Z - 1), Z and (Z + 1) respectively. B is an inert gas (not helium). What is the group number of element A?

Answer 1

'B' belongs to noble gas family or 18th group. The element having atomic number $1$ less than that of inert gas belongs to ${17}^{th}$ group.

Thus, $A$ belongs to ${17}^{th}$ group.