An element P(atomic number 20) reacts with an element Q (atomic number 17) to form a compound. Answer the following questions giving reasons :
(a) Write the positions of P and Q in the Modern Periodic Table.
(b) Write the molecular formula of the compound when P reacts with Q.

Explanation

(a) The electronic configuration of the elements P and Q are as follows :
P (Z = 20) 2, 8, 8, 2, Q (Z = 17) 2, 8, 7 The element P (Ca) is present in group 2 and period 4 whereas Q (Cl) belongs to group 17 and period 3.
(b) The molecular formula of the compound is `PQ_(2)." It is "CaCl_(2).`