Question

the number of electrons in the outermost shell of chlorine is 7 what is its valency and why

Answer 1

Its valency is considered to be 1.
Because it needs just one electrons in its outermost shell to be stable.

hope it helps u

Answer 2

Although it has 7 elecctron in its valance shell but its valency will be -1 because it has tendency to gain one electron it cannot donate its electron because it needs lotvof energy to remove an electron from the chlorine