The correct answer is option 1, Agaricus. Agaricus is a type of fungus that is dependent on a saprophytic mode of nutrition. Saprophytic organisms obtain their nutrition by decomposing dead organic matter. In the case of Agaricus, it obtains its nutrients by breaking down and decomposing dead plant material, such as leaves and wood.

Option 2, Ulothrix, is a type of green alga that is not dependent on saprophytic mode of nutrition. Green algae are typically autotrophic, meaning they can produce their own food through photosynthesis.

Option 3, Riccia, is a type of liverwort, which is a small, non-vascular plant. Liverworts can obtain their nutrients through various mechanisms, including through their symbiotic relationship with fungi, but they are not strictly saprophytic.

Option 4, Cladophora, is a type of green alga that is also not dependent on a saprophytic mode of nutrition. Like Ulothrix, it is capable of photosynthesis and can produce its own food.

Overall, only Agaricus out of the given options is a saprophytic organism.