Final answer:
AgCl is the compound insoluble in water among the ones listed. Most ionic salts are soluble, but there are specific rules where certain halides are not, and AgCl is an example of this exception.
Step-by-step explanation:
The compound AgCl (silver chloride) is insoluble in water. Most ionic salts are generally soluble in water, but there are exceptions like AgCl which is characterized by its physical state notation 's' showing that it is solid and not significantly soluble in water. Rules of solubility indicate that while many nitrates, chlorates, and acetates are soluble, halides like chlorine, bromine, and iodine can be insoluble if they are paired with ions such as silver (Ag+), lead (Pb2+), or mercury (Hg2+). Therefore, out of the compounds listed, CaCl2, KCl, and AgNO3 are all soluble in water, but AgCl is the one that is insoluble.