Ethylene is a

Options

A. A gaseous metabolite
B. A gaseous enzyme
C. A gaseous hormone
D. A solid hormone.

Answer

**Step-by-Step Solution:**

1. **Understanding Ethylene**: Ethylene is a compound that plays a significant role in plant biology. It is important to identify its classification correctly.

2. **Options Analysis**: The question provides four options:
- Gaseous metabolite
- Gaseous enzyme
- Gaseous hormone
- Solid hormone

3. **Definition of Hormones**: Hormones are biochemicals that are produced in one part of an organism and have effects on other parts. They target specific cells or organs and are crucial for regulating various physiological processes.

4. **Definition of Enzymes**: Enzymes are biocatalysts that speed up chemical reactions in living organisms by lowering the activation energy required for those reactions.

5. **Identifying Ethylene's Role**: Ethylene is known to be involved in several plant growth processes, including:
- Seed germination
- Fruit ripening
- Response to environmental stresses

6. **Conclusion**: Given that ethylene is involved in these hormonal functions and is known to exist in a gaseous state, the correct classification of ethylene is as a "gaseous hormone."

7. **Final Answer**: The correct option is **gaseous hormone**.

---