Name a phytohormone which is gaseous in nature.

Explanation

**Step-by-Step Solution:**

1. **Understanding Phytohormones**: Begin by defining what phytohormones are. Phytohormones, also known as plant hormones, are chemical substances that regulate various physiological processes in plants.

2. **Identifying Types of Phytohormones**: Recognize that there are several types of phytohormones, including auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

3. **Focus on Gaseous Nature**: The question specifically asks for a phytohormone that is gaseous in nature. This requires us to filter through the types of phytohormones to identify which one exists in a gaseous state.

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