This is pretty simple, just give me a quick concept should be enough, no need to go over the details. What determines the radius size again? Was it just the electrons? Say for example which is bigger, potassium ion or argon. Same electron configuration but different proton numbers. Would the extra proton pull the electrons to make it smaller for potassium or would the extra proton make the radius bigger. This isnt homework or anything, use another example if you want.