What is an example of a halogen agent used in fire extinguishers?

A halogen agent is a type of fire extinguishing agent that is based on halogen compounds, which are effective in interrupting the chemical reactions that occur during combustion. In this context, option C, 1211, refers to carbon tetrachloride, which was historically used as a fire suppression agent due to its ability to inhibit the fire triangle by removing heat or interrupting the chemical chain reaction. It is a member of the halogenated compounds that target Class B and Class C fires.

The other options do represent fire extinguishing agents, but they do not fall under the category of halogen agents. Potassium bicarbonate and sodium bicarbonate are dry chemical agents primarily used for Class B fires, while carbon dioxide is another gas used for Class B and Class C fires, focusing on displacing oxygen rather than utilizing halogen chemistry. Thus, 1211 stands out as the correct choice when identifying a halogen agent.