Final answer:
The oxidizing agent that helps to develop hair color or lightener is Developer. It oxidizes the dye precursors and causes them to react with coupling agents, resulting in the formation of the final dye.
Step-by-step explanation:
The oxidizing agent that helps to develop hair color or lightener is c) Developer. In the process of permanent hair coloring, the developer is responsible for oxidizing the dye precursors and causing them to react with the coupling agents, resulting in the formation of the final dye. The most common oxidizing agent used in hair color products is hydrogen peroxide.