Concept:Hygroscopic substances absorb moisture from the air. Among fertilizers, urea is known to be highly hygroscopic.Explanation:Urea rapidly absorbs moisture from the air, especially in high humidity. For this reason, it must be stored in sealed or closed bags. Urea has the highest nitrogen content (46%) among the given options. Other nitrogenous fertilizers like calcium ammonium nitrate (20.5–25% nitrogen), sodium nitrate (16% nitrogen), and ammonium sulphate (21% nitrogen) are less hygroscopic and do not absorb moisture as readily as urea does.Answer:D. Urea