A co-enzyme can be:

Options

A. conjugated protein
B. organic molecule
C. inorganic ion
D. metal

Answer

**Step-by-Step Solution:**

1. **Understanding Coenzymes**: Coenzymes are non-protein molecules that assist enzymes in catalyzing reactions. They are essential for the activity of many enzymes.

2. **Identifying Coenzymes**: Coenzymes can be classified as organic molecules. They are often derived from vitamins and are necessary for the proper functioning of enzymes.

3. **Differentiating from Other Options**:
- **Conjugated Protein**: This is incorrect because coenzymes are not proteins; they are non-protein molecules.
- **Inorganic Ions**: While some cofactors can be inorganic ions (like metal ions), coenzymes specifically refer to organic molecules.
- **Metal Ions**: Similar to inorganic ions, metal ions are not classified as coenzymes; they are considered separate types of cofactors.

4. **Conclusion**: Based on the definitions and classifications, the correct answer to the question "A co-enzyme can be:" is **organic molecule**.

**Final Answer**: Organic molecule

---