Final answer:
Sodium hypochlorite is the commonly used biocide for sulfide-contaminated systems due to its ease of handling compared to chlorine gas and its effectiveness as a strong oxidizing agent.
Step-by-step explanation:
The biocide used for sulfide-contaminated systems is often a chlorine-based compound. The most common chlorine-based biocides include sodium hypochlorite, which is the chemical component of common household bleach, and chlorine gas itself. Chlorine is highly effective due to its strong oxidizing properties, which allow it to disrupt cellular components in microbial organisms. Sodium hypochlorite is a particularly practical choice as it is easier to store and handle compared to chlorine gas. Other agents such as hydrogen peroxide and quaternary ammonium compounds are also used in different contexts for their antimicrobial properties, but chlorine compounds remain prevalent for disinfection in water treatment.