Taxonomists feel difficulty in classification of :-

Options

A. Prokaryotes
B. Unicellular eukaryotes
C. Plants
D. Animals

Answer

### Step-by-Step Solution

1. **Understanding the Question**: The question asks about the difficulty taxonomists face in classifying certain groups of organisms. The options provided are prokaryotes, unicellular eukaryotes, plants, and animals.

2. **Analyzing the Options**:
- **Prokaryotes**: These organisms lack a true membrane-bound nucleus and have simpler cellular structures. Their classification is relatively straightforward due to these distinct characteristics.
- **Unicellular Eukaryotes**: These organisms have a true nucleus and can exhibit a wide variety of nutritional modes, including autotrophic (like plants), heterotrophic (like animals), and decomposer roles (like some algae). This diversity makes their classification challenging.
- **Plants**: These are multicellular eukaryotes with a cell wall and primarily autotrophic nutrition. Their characteristics are well-defined, making classification easier.
- **Animals**: Like plants, animals are multicellular eukaryotes but are heterotrophic and lack a cell wall. Their distinct characteristics also facilitate classification.

3. **Identifying the Correct Answer**: Given the analysis, unicellular eukaryotes present the most difficulty in classification due to their diverse nutritional strategies and similarities to both plants and animals.

4. **Conclusion**: Therefore, the correct answer is **unicellular eukaryotes**.