Position of three elements A, B and C in the periodic table is shown below :

Giving reasons explain :
(a) Element A is a metal.
(b) Element B has larger atomic size than the element C.
(c) Element C has a valency of one.

Explanation

(a) Element A belongs to group I and period 3. It is sodium (Na) and is a metal.
(b) We know that the atomic size of the elements decreases along a period and increases down a group. The element B (group II and period 3) has larger atomic size than the element C (group II and period 2).
(c) Element C is a member of halogen family. It is fluorine (F) and its valency is 1 (8 - 7 = 1).