Final answer:
Formalin, which contains about 37% formaldehyde, is primarily used to fix tissues for histology in veterinary hospitals as it preserves tissue specimens by killing bacteria and halting decay.
Therefore, option C is correct.
Step-by-step explanation:
Formalin is most commonly used for fixing tissues for histology in the veterinary hospital. Formalin, which is an aqueous solution containing about 37% formaldehyde, serves as a tissue fixative. The formaldehyde in formalin causes coagulation of proteins, which kills bacteria and stops biological processes that would otherwise cause tissue to decay. This property makes it ideal for preserving tissue specimens and embalming, but due to its irritating and carcinogenic nature, it is not used as an antiseptic. While formaldehyde can be a sterilant and is used in some disinfection processes, its primary use in veterinary settings is for preserving tissue specimens to be examined later under a microscope.