A farmer is growing a crop regularly in his field. He uses chemical fertilizers, pesticides, organic manure as well as bio-fertilizers. Very close to his field is a factory which emits smoke as a by product. There is also a huge lake in the nearby area.
A considerable increase in plant life in the lake was noticed after the farming activity intensified. The most likely reason for this could be:

Options

A. Chemical fertilizers leached into the lake from the field.
B. Pesticides leached into the lake from the field.
C. Organic manure leached into the lake from the field.
D. Smoke particles from the industry got settled in moist surroundings of the lake.

Explanation

To answer the question regarding the increase in plant life in the lake after the farmer intensified his farming activities, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**:
- The farmer is using various agricultural inputs including chemical fertilizers, pesticides, organic manure, and bio-fertilizers.
- There is a factory nearby that emits smoke, and there is a lake close to the field.

2. **Identifying the Changes**:
- After the farming activities intensified, there was a noticeable increase in plant life in the lake.

3. **Analyzing the Possible Causes**:
- The key point is to determine what could have caused the increase in plant life in the lake.
- The options provided include:
- A) Chemical fertilizers leached into the lake from the field.
- B) Pesticides leached into the lake from the field.
- C) Organic manure leached into the lake from the field.
- D) Smoke particles from the industry settled in the lake.

4. **Evaluating Each Option**:
- **Option A (Chemical fertilizers)**: This is a strong possibility. Chemical fertilizers are rich in nutrients like nitrogen and phosphorus, which can run off from the field into the lake, promoting plant growth, particularly algae. This process is known as eutrophication.
- **Option B (Pesticides)**: While pesticides may leach into the lake, they do not provide nutrients necessary for plant growth.
- **Option C (Organic manure)**: Organic manure does not contain the same concentrated nutrients as chemical fertilizers, and its leaching would not significantly contribute to the increase in plant life.
- **Option D (Smoke particles)**: Smoke from the factory does not provide nutrients and would not explain the increase in plant life.

5. **Conclusion**:
- The most likely reason for the considerable increase in plant life in the lake is due to **chemical fertilizers leaching into the lake from the field**.

### Final Answer:
The most likely reason for the considerable increase in plant life in the lake is **A) Chemical fertilizers leached into the lake from the field**.