Which of these is a non-combustible substance?

Options

A. Sand
B. Wood
C. Paper
D. Petrol

Answer

To determine which of the given substances is non-combustible, we can analyze each option based on their ability to burn in the presence of air.

### Step-by-Step Solution:

1. **Identify the Options**: The options provided are sand, wood, paper, and petrol.

2. **Evaluate Each Substance**:
- **Sand**: Sand is a mineral and does not burn. It does not react with air to produce combustion. Therefore, sand is a non-combustible substance.
- **Wood**: Wood is an organic material that burns easily in the presence of air. It is a combustible substance.
- **Paper**: Similar to wood, paper is made from organic materials and burns readily in the presence of air. Thus, it is also a combustible substance.
- **Petrol**: Petrol is a liquid hydrocarbon that ignites and burns in the presence of air. Therefore, it is a combustible substance.

3. **Conclusion**: Among the options, only sand does not burn in the presence of air. Therefore, the correct answer is that sand is a non-combustible substance.

### Final Answer:
The non-combustible substance is **sand**.

---