Ecotone is :

Options

A. A polluted area
B. The bottom of a lake
C. A zone of developing community
D. A zone of transition between two communities

Answer

### Step-by-Step Text Solution:

1. **Definition of Ecotone**: An ecotone is a transitional area between two distinct ecosystems. It serves as a boundary where two different ecological communities meet and interact.

2. **Examples of Ecotones**: A common example of an ecotone is the area where a forest ecosystem meets a grassland ecosystem. This region will have characteristics of both ecosystems.

3. **Characteristics of Ecotones**:
- Ecotones contain species and elements from both bordering ecosystems.
- They often have a higher biodiversity than the individual ecosystems due to the mixing of species.

4. **Options Analysis**:
- Option 1: A polluted area - This is incorrect as ecotones are not defined by pollution.
- Option 2: Bottom of a lake - This is also incorrect as it does not represent a transitional area between ecosystems.
- Option 3: A zone of developing communities - This is incorrect; ecotones are not specifically zones of developing communities.
- Option 4: A zone of transition between two communities - This is the correct definition of an ecotone.

5. **Conclusion**: Based on the analysis, the correct answer is that an ecotone is a zone of transition between two communities (Option 4).