Potassium is the most reactive element as it is a metal as well as a strong alkali. Chlorine is a little less reactive than potassium but higher than argon. Argon being a noble gas is not reactive at all as all its shells are filled by electrons.
The Electron Configurations Of Argon Differs From Those Of Chlorine And Potassium By One Electron Each. Compare Reactivity Of These Three Elements And Relate Them To Their Electron Configurations?