One of the following is not a combustible substance. This one is :

Options

A. alcohol
B. hydrogen
C. asbestos
D. chaff

Answer

To determine which of the following substances is not a combustible substance, we need to understand what a combustible substance is.

### Step-by-Step Solution:

1. **Definition of Combustible Substance**:
- A combustible substance is one that can burn in the presence of air (oxygen) and produce heat and light.

2. **Identifying Combustible Substances**:
- Common examples of combustible substances include:
- Alcohol
- Hydrogen
- Charcoal (often referred to as "shaft" in the transcript)
- All of these substances can burn and produce heat and light when ignited.

3. **Identifying Non-Combustible Substance**:
- Asbestos is mentioned in the transcript as a material that does not burn.
- It is used as a fire-resistant material and does not produce heat or light when exposed to fire.

4. **Conclusion**:
- Among the options provided, asbestos is the substance that is not combustible.

### Final Answer:
- The substance that is not a combustible substance is **Asbestos**.

---