Question

Elements of group 1 have and elements of group 17 the valency have 1 explain why

Answer 1

as group 1 contain 1 valence electrons and group 17 contain 7 valence electrons
if valence electrons is more than 4
than we subtract it from 8 for finding valency or leave it if it's less than 4
:. valency be 1

Answer 2

elements of group 1 and group 17 have 1 and 7 valence electrons respectively.
we know that valency= 1,2 ,3 so valency of group one element =1
also valency = 8-no of valence electrons if it is greater than 3
so valency of group 17 elements is also 1
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