Chlorine can exhibit `-1` and `+1` states, while fluorine can exhibit only `-1`, but not `+1`. Why?

Explanation

General valency of halogens is one. When chlorine (or bromine or iodine) is mono-valent, with more electronegative elements, it exhibits `+ 1` state.
Fluorine can never exhibit positive oxidation state as it is the most electronegative element.