Compared to a potassium atom, a potassium ion has
(1) a smaller radius
(2) a larger radius
(3) fewer protons
(4) more protons
Answer and Explanation: Let's first look at the Periodic Table on the reference sheet to find out what kind of ion does potassium have? If we look at the top right of K (potassium), we see the charge plus 1. Therefore, the ion of potassium has a +1 charge. +1 charge means that potassium atom has lost 1 electron. Therefore, a potassium ion has a smaller radius since it has less electrons.
P.S. The number of protons gives the identity of the element. Therefore, an atom or an ion of potassium must always have the same number of protons (19).