Given below are some elements of the Modern Periodic Table:
`""_(4)Be, ""_(26)Fe.""_(14)Si, ""_(19)K ""_(20)Ca`
i) Select the element that has one electron in the outermost shell and write its electronic configuration.
ii) Select two elements that belong to the same group. Give reason.
iii) Select two elements that belong to the same period. Which one of the two has a bigger atomic size?

Explanation

(i) `_(19)K` (Potassium) is the element that has one electron in the outermost shell.
Electronic configuration = 2,8,8,1 (ii) `_(4)Be` (Beryllium) and `_(20)Ca` (Calcium) belong to the same group, because they have same number of valence electrons.
Be = 2, 2 and Ca = 2, 8, 8, 2 (iii) Berylium (Be) and Fluorine (F) have same period i.e., second period which has 2 shells (K and L) whereas Potassium (K) and Calcium (Ca) also belong to same period i.e., fourth period which have 4 shells (K, L, M and N).