Final answer:
Potassium chloride (KCl) is not an insoluble compound; it is soluble in water according to solubility rules, while calcium carbonate, calcium phosphate, and iron (III) oxide are typically insoluble.
Step-by-step explanation:
The objective of this exercise is to determine which of the given compounds is not insoluble. To do that, we need to understand the general rules of solubility for ionic compounds.
Let's look at the compounds listed:
Calcium carbonate (CaCO3)
Potassium chloride (KCl)
Calcium phosphate (Ca3(PO4)2)
Iron (III) oxide (Fe2O3)
Based on the solubility rules, most compounds containing the alkali metal ions (such as potassium) and the ammonium ion (NH4+) are soluble. Thus, potassium chloride (KCl) is a soluble compound.
The remaining options are typically insoluble: calcium carbonate, calcium phosphate, and iron (III) oxide do not readily dissolve in water. Hence, the compound that is not an insoluble compound in the list provided is potassium chloride.