Concept:Deliquescence is an extreme form of absorbing atmospheric moisture, which makes it a type of hygroscopic behaviour.Explanation:A deliquescent substance absorbs water vapour from the air until it dissolves into a solution.This absorption of moisture is the defining property of hygroscopic substances.All deliquescent substances are therefore hygroscopic because they take up moisture from the atmosphere.However, not all hygroscopic substances are deliquescent, since many only absorb moisture without dissolving.The option that correctly describes deliquescent substances is hygroscopic.Answer:C. hygroscopic