Question

elements of group first n elements of group 17 both have valency one?

Answer 1

yes becuase
the elements of group one have one electron in the outermost shell
so valency =1
and group 17 has 7 electrons
so valency =8-7=1

Answer 2

group 1 elments have tendency to loose one electron to achieve stability.
And group 17 elements have tendency to accept one electron to complete octet for stability