A reaction between certain organic compounds and free chlorine can form what?

The reaction between certain organic compounds and free chlorine can indeed result in the formation of trihalomethanes (THMs). This occurs during a process known as chlorination, where chlorine reacts with natural organic matter such as humic substances present in water. This interaction can lead to the creation of several by-products, among which THMs are significant due to their potential health risks when consumed in drinking water.

THMs, including chloroform, bromoform, bromodichloromethane, and dibromochloromethane, are of particular concern because they are classified as possible human carcinogens. Their presence in treated drinking water is regularly monitored, and water treatment facilities often take measures to minimize their formation.

While other options such as chloramines, haloacetic acids (HAAs), and chlorinated solvents can also be products of chlorine reactions with organic compounds or other substances, THMs specifically arise from the chlorination of organic matter in water treatment and are therefore the correct choice in this context.