From the following elements : ""_(4) Be,""_(9) K, ""_(20) Ca (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 ""_(19) K and element X(2, 8, 7).

From the following elements : ""_(4) Be,""_(9) K, ""_(20) Ca (i) sel

1.	From the following elements : ""_(4) Be,""_(9) K, ""_(20) Ca (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 ""_(19) K and element X(2, 8, 7).
Answer» Solution :(i) `""_(19) K` has one electron in the outermost shell. It has the electronic configuration : `2,8,8,1` `""_(4) Be and ""_(20) Ca` belong to Group 2. Both of them have two electrons in the outermost shell and therefore belong to Group 2 (same group). Formula of the compound formed by the UNION of `""_(19) K and X(2, 8, 7)` is : `KX`. Nature of the compound will be IONIC because K (2, 8, 8, 1) will donate one electron to X. This will complete the octet of both.