What is the disinfectant and preservative commonly found in hardening compounds?

The correct answer is paraformaldehyde, which is a stabilized form of formaldehyde and is commonly used in hardening compounds due to its properties as both a disinfectant and preservative. Paraformaldehyde is effective in embalming by enhancing tissue preservation and providing rigidity to the body, making it particularly suitable for the hardening process in embalming fluids and compounds.

Formaldehyde, while also a powerful disinfectant and preservative, is typically found in gas or solution form rather than in hardening compounds. Phenol is well-known for its antiseptic qualities and is used in some embalming fluids but does not serve the same purpose within hardening compounds. Glutaraldehyde is another alternative used in some disinfection processes and is less commonly associated with hardening compounds compared to paraformaldehyde. Thus, the nature and application of paraformaldehyde make it the appropriate choice for this specific context.