The International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet because it did not meet the three criteria the IAU uses to define a full-sized planet. Essentially Pluto meets all the criteria except one—it “has not cleared its neighboring region of other objects.”
The word missing is ionic. Ionic compounds are soluble to water. They are soluble because water is a polar molecule. Water has a positive end and a negative end. These ends attract ionic compounds. However, not all ionic compounds are able to dissolve in water.