## Explanation

### Volume

When discussing the **concentration and strength of hydrogen peroxide**, "Volume" is the unit used to measure it. Hydrogen peroxide is often used in various concentrations, especially in the beauty and haircare industry. The term "Volume" in this context specifically refers to the amount of oxygen gas that would be released from the solution.

For example, a **20 Volume** hydrogen peroxide solution will release 20 volumes of oxygen gas for every one volume of the solution. This is significant when using hydrogen peroxide in beauty treatments such as **baliage**, which requires careful control of the developer's strength.

The relationship can be mathematically represented by:

$\text{Volume 50} \quad \text{contains} \quad 15\% \quad \text{H}_2\text{O}_2$ $\text{Volume 30} \quad \text{contains} \quad 9\% \quad \text{H}_2\text{O}_2$ $\text{Volume 20} \quad \text{contains} \quad 6\% \quad \text{H}_2\text{O}_2$ $\text{Volume 10} \quad \text{contains} \quad 3\% \quad \text{H}_2\text{O}_2$Therefore, the **Volume** measurement is crucial in determining how potent the hydrogen peroxide is, which affects both the chemical reactions and the safety of its usage.