Final answer:
Hydrogen peroxide is the most commonly used developer or oxidizing agent for both hair treatments, such as bleaching and dying, and as a household disinfectant.
Step-by-step explanation:
The most commonly used developer or oxidizing agent, especially in the context of hair treatments and household disinfectants, is hydrogen peroxide (H₂O₂). It is widely used due to its effectiveness and since it breaks down into water and oxygen gas, making it environmentally safe. In the beauty industry, diluted hydrogen peroxide is used for bleaching hair, earning the phrase "peroxide blonde". It is also a part of the permanent hair coloring process where it serves as the oxidant that helps to develop the final dye. Additionally, it is found in whiteners such as toothpaste due to its bleaching properties. For disinfection purposes, hydrogen peroxide is sold as a 3% by volume solution, showcasing its broad utility.