Final answer:
Potassium bromide (KBr) is soluble in water according to solubility rules, because potassium is an alkali metal.
Step-by-step explanation:
To determine whether the compound potassium bromide (KBr) is soluble or insoluble, we refer to the general solubility rules for common ionic compounds. According to these rules, all compounds containing alkali metal cations and the ammonium ion are soluble in water. Since potassium (K) is an alkali metal, compounds containing potassium, such as KBr, are typically soluble. Therefore, KBr is classified as a soluble compound in water.