Which substance is not a surface active agent?

EDTA, or ethylene diamine tetraacetic acid, is primarily a chelating agent, meaning it binds to metals and helps to remove them from solutions. It works by forming stable complexes with metal ions, which enhances the solubility of those metals and prevents them from participating in chemical reactions. While it does have some applications in cleaning and can indirectly contribute to surface activity by removing metal-induced hardness in water, it does not function primarily as a surface-active agent.

In contrast, substances like soap, detergents, and surfactants are specifically designed to lower the surface tension of water, allowing them to break down oils and dirt more efficiently. They work by orienting themselves at the interface between water and oil (or other substances), where their hydrophilic (water-attracting) and hydrophobic (water-repelling) characteristics enable them to emulsify, disperse, and solubilize various substances. Therefore, while EDTA has its unique role in various chemical processes and cleaning applications, it does not share the fundamental characteristics of a surface-active agent.