From the following elements : _(4)Be,_(9)F,_(19)K,_(20)Ca (i) Select the element having one electron in the outermost shell. (ii) Two elements of the same group. Write the formula 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)F,_(19)K,_(20)Ca (i) Select

1.	From the following elements : _(4)Be,_(9)F,_(19)K,_(20)Ca (i) Select the element having one electron in the outermost shell. (ii) Two elements of the same group. Write the formula and mention the nature of the compound formed by the union of _(19)K and element X (2,8,7).
Answer» Solution :(i) The elements which have one ELECTRON in the outermost shell are `_(19)K=2,8,8,1` (II) Two elements of the same GROUP are Beryllium (Be) and Calcium (CA). `_(4)Be=2,2` `_(20)Ca=2,8,8,2` Formula of element K and element X: Both elements K and X have valency one. So, It is an electrovalent COMPOUND.