Which of these will neutralize ptomaines?

The correct choice is methanal, also known as formaldehyde, which plays a role in neutralizing ptomaines. Ptomaines are nitrogenous organic compounds that can cause food poisoning and are typically formed during the decomposition of proteins. Formaldehyde has strong antimicrobial properties and can effectively react with these compounds to neutralize their toxic effects.

Using formaldehyde as an antifungal and antimicrobial agent emphasizes its role in preserving biological specimens and food products, thus preventing the formation of ptomaines or neutralizing existing ones.

While acetic acid can also serve as a mild disinfectant, it does not have the same level of effectiveness when it comes to neutralizing ptomaines compared to formaldehyde. Ethylene glycol, primarily used in antifreeze, and other unrelated compounds do not possess properties that neutralize these toxic substances effectively.