The electronic configuration of four elements A,B,C and D is given as follows:

A-2,8 B-2,8,1


C-2,8,2 D-2,8,8


a. Which of them belong to the same period? Name the period.


b. Which of them belong to the same group? Name the group.

(a) We know that elements with same number of shells are placed in same period and period is equal to the number of shells contain. So elements B, C and D belong to same period and the period is 3.


(b) We know that those elements which have same electrons in outermost shell belong to same group. So elements A and D belong to same group. And there are 8 electrons in outermost shell so the group is 18.


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