Valency of chlorine is 1.
What is Valency?
Valency is basically the number of electrons gained, lost or shared by an atom of an element to achieve the nearest noble gas configuration or stable configuration.
Coming to chlorine, it needs just one more electron to reach the Argons’ configuration i.e octet configuration.
Chlorine’s electronic configuration is Ne3s23p5 and if it gets one electron, then it will get a 3s23p6 stable octet configuration.
Thus valency of chlorine is 1.