Final answer:
Ba+2 is the ion most attracted to water due to its higher charge density, which stems from its +2 charge and smaller radius compared to Ra+2.
Step-by-step explanation:
The student's question asks: Which of the following ions is most attracted to water? A) Cs+1 B) Rb+1 C) Ba+2 D) Ra+2. Water molecules are polar, with a slight positive charge on the hydrogen atoms and a slight negative charge on the oxygen atom, which allows water to attract ions. The attraction of an ion to water molecules is termed hydration and largely depends on the charge density of the ion. Charge density is the charge of an ion divided by its volume.
The more highly charged an ion and the smaller its radius, the greater its charge density, which increases its attraction to water. Comparing the ions listed, Ba+2 and Ra+2 have a +2 charge, which is higher than the +1 charge of Cs+1 and Rb+1. Generally, Ba+2 would be smaller in size than Ra+2, as radium is below barium in the periodic table and atomic size increases down a group. Therefore, Ba+2 will have a higher charge density and be most attracted to water among the options given.