Question

which is more non metallic S or CL and why

Answer 1

If you are so keen on explaining it then know that metalic character decreases up the group and across the period. So that means that sulphur is ever so slightly more metalic than chlorine. However in real life this makes no sense as both are one of the most charachteristic non metals we know.

Answer 2

chlorine .. because when we move across the period non metallic characterstics increases..( tendency to gain electrons increases)