Question

State why $Na$ has a electropositive valency of $+1$ and $Cl$ an electronegative valency of $-1$.

Answer 1

$Na$ has $2,8,1$ configuration so it will looses one electron and gains octet configuration so it has valency of $+1$ while $Cl$ has configuration of $2,8,7$ and to complete octet, it gains one electron so its valency is $-1$.