Concept:Ammonia is a basic gas, so the drying agent must be basic and must not react with it.Explanation:Calcium chloride reacts with ammonia to form a complex, so it cannot be used.Phosphorus(V) oxide and concentrated H2SO4 are acidic and will react with ammonia.Calcium oxide, CaO, is a basic drying agent and does not react with ammonia.Therefore, the suitable drying agent for ammonia is calcium oxide.Answer:B. Calcium Oxide