A heap of green leaves is lying in one corner of a park. The green leaves in the heap burn with difficulty because :

Options

A. they contain a tough material called cellulose
B. they contain a lot of water
C. they contain a green pigment chlorophyll
D. they do not get sufficient oxygen for burning

Answer

### Step-by-Step Solution

1. **Understanding the Question**: The question states that a heap of green leaves is lying in a park and that these leaves burn with difficulty. We need to identify the reason for this difficulty in burning.

2. **Identifying the Composition of Green Leaves**: Green leaves contain a significant amount of water. This is an important factor to consider when analyzing why they burn poorly.

3. **Understanding Ignition Temperature**: The ignition temperature is the minimum temperature required for a substance to ignite and start burning. For combustion to occur, the material must reach this temperature.

4. **Analyzing the Effect of Water**: The presence of a lot of water in green leaves prevents them from reaching their ignition temperature. Water absorbs heat and requires energy to evaporate, which means that the leaves cannot get hot enough to ignite.

5. **Evaluating the Options**:
- **Option 1**: They contain a tough material called cellulose. This is incorrect because cellulose does not directly cause difficulty in burning.
- **Option 2**: They contain a lot of water. This is correct as it prevents the leaves from reaching their ignition temperature.
- **Option 3**: They contain a green pigment called chlorophyll. This is incorrect as chlorophyll does not affect the burning process.
- **Option 4**: They do not get sufficiently oxygen for burning. This is incorrect because the main issue is the water content, not the availability of oxygen.

6. **Conclusion**: The correct answer is that the green leaves burn with difficulty because they contain a lot of water, which prevents them from reaching their ignition temperature.

### Final Answer
The green leaves in the heap burn with difficulty because they contain a lot of water, which prevents them from reaching their ignition temperature.