Final answer:
The pair KI and Ba(NO3)2 (option D) is soluble in water because it contains compounds that follow the solubility rules, with KI having an alkali metal ion and Ba(NO3)2 containing the nitrate ion.
Step-by-step explanation:
The question asks which pair of compounds is soluble in water. Solubility rules for ionic compounds in water indicate that all nitrates are soluble and that salts containing alkali metal cations are typically soluble as well. Therefore, the pair D) KI and Ba(NO3)2 is soluble in water because potassium iodide (KI) includes an alkali metal ion (K+), and barium nitrate (Ba(NO3)2) contains the nitrate ion (NO3-), which are both soluble according to the solubility rules. Compounds containing the acetate ion (CH3COO-), nitrate ion (NO3-), and the ammonium ion (NH4+) are generally soluble in water. In contrast, compounds like silver bromide (AgBr) and cadmium sulfide (CdS) are generally insoluble except for a few specific exceptions.