What pollutant is commonly associated with metal finishing processes?

Cyanide is commonly associated with metal finishing processes because it is often used in electroplating and other processes to help create a smooth and corrosion-resistant finish on metals. In these applications, cyanide serves as a complexing agent that helps stabilize metal ions in solution, enabling better plating quality. The presence of cyanide in wastewater from metal finishing operations is a significant environmental concern due to its toxicity. Regulations often target the treatment and proper handling of cyanide to prevent contamination of water sources.

The other pollutants listed, such as lead, mercury, and arsenic, can also be associated with various industrial processes, but cyanide is specifically highlighted for its role and common use in metal finishing, distinguishing it as the correct choice in this context.