Elements A, B, C, D and E have the electronic configura-tion as shown in the table :

(i) Name the element which belongs to the `2^(nd)` period.
(ii) Name two elements which will exhibit a valency of 1.
(iii) Name another element which will have the same valency as the element C.

Explanation

(i) The element A belongs to the `2^(nd)` period since the electrons are filled K and L shells only.
(ii) The elements B and D exhibit valency of 1. Valency of element B = 1, Valency of element D = (8 - 7) = 1.
(iii) The element A has the same valency as the element C. Valency of element C = (8 - 5) = 3, Valency of element A = 3. Therefore, both of them have the same valency.