The correct answer is A. Aqueous is formaldehyde.
Formalin is a 37% aqueous solution of formaldehyde. It is a colorless, pungent-smelling liquid that is used as a preservative, disinfectant, and embalming fluid. Formaldehyde is also used in the production of plastics, resins, and other chemicals.
Ferrous sulfate is a green, water-soluble salt that is used as a fertilizer, wood preservative, and in the manufacture of other chemicals. Formic acid is a colorless, flammable liquid that is used in the production of plastics, resins, and other chemicals. Ferric alum is a brown, water-soluble salt that is used as a mordant, astringent, and in the manufacture of other chemicals.
Dead organs are usually kept in formalin to prevent them from decaying. Formalin is a strong preservative that kills bacteria and other microorganisms that can cause decomposition. It also helps to prevent the release of unpleasant odors.