. From the following elements
4Be; 9F; 19K; 20Ca
(i) Select the element having one electron in the .outermost shell.
(ii) two elements of the same group.
Write the formula of and mention the nature of the compound formed by the union of 19K and element X(2,8,7).
Ans. (i) 19K
(ii) 4Be, 20Ca belong to the same group.
Electronic configuration of K (19) = 2, 8, 8, 1 Valency of K = 1
Electronic configuration of X (2, 8, 7) Valency of X = 1