ACS Analytical Chemistry Practice Exam

Masking agents in EDTA complexometric titration serve to suppress interference from certain metal ions by binding them so they cannot react with EDTA. This sequestering allows the titration to target the ion of interest without EDTA being consumed by other metals present in the solution. The option describes exactly this protective role—keeping an interfering component from reacting with EDTA—so it best explains the purpose of a masking agent. It isn’t about speeding the reaction with all metals, changing the endpoint color, or increasing solubility of interferents.