Answer:
Explanation:
When we go down in a column , we are going down in a period . In going down , one additional orbit go on adding to the atom . But the total number of electrons in the outermost orbit which is also called valence electron remains the same .
For example , when we go down in the first group A , the outermost orbit go on changing like 1 s¹ , 2 s¹ , 3 s¹ . 4 s ¹ etc which represents hydrogen , lithium . sodium , potassium etc.
So we see that , it is number of valance electrons that remains constant.
