Given below are some elements of the modern periodic table :
`""_(4)Be, ""_(9)F,""_(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 for your answer.
(iii) Select two elements that belong to the same period. Which one of the two has bigger atomic size ?

Explanation

The electronic distribution of the elements are :
`""_(4)Be(2,2), ""_(9)F(2,7),""_(14)Si(2,8,4),""_(19)K(2,8,8,1),""_(20)Ca(2,8,8,2).`
(i) The elements is potassium (K).
(ii) The elements Be and Ca belong to second group since their atoms have two electrons in the valence shell.
(iii) The elements belonging to the same period are Be and F (belong to second period) , K and Ca (belong to fourth period).
The element Be has bigger size than F since atomic size decreases along a period.
The element Ca has smaller size because of the same reason.