Which one of the following is a peptide hormone ?

Options

A. Glucagon
B. Testosterone
C. Thyroxin
D. Adrenaline

Explanation

To determine which of the given options is a peptide hormone, we can follow these steps:

### Step-by-Step Solution:

1. **Understand What a Peptide Hormone Is**:
- Peptide hormones are hormones that are made up of amino acids linked together by peptide bonds. They are typically secreted by glands in the body and play various roles in regulating physiological processes.

2. **Analyze the Given Options**:
- We need to evaluate each option to see if it qualifies as a peptide hormone.

3. **Evaluate Option 1: Glucagon**:
- Glucagon is a hormone secreted by the pancreas. It is composed of 29 amino acids linked by peptide bonds, which classifies it as a peptide hormone.

4. **Evaluate Option 2: Testosterone**:
- Testosterone is a steroid hormone, not a peptide hormone. It is derived from cholesterol and is primarily associated with male sexual characteristics.

5. **Evaluate Option 3: Thyroxine**:
- Thyroxine is a thyroid hormone that contains iodine. It is not a peptide hormone; it is a derivative of the amino acid tyrosine and is classified as an amine hormone.

6. **Evaluate Option 4: Adrenaline**:
- Adrenaline (also known as epinephrine) is produced by the adrenal glands and acts as both a hormone and a neurotransmitter. It is derived from the amino acid tyrosine and is not classified as a peptide hormone.

7. **Conclusion**:
- After evaluating all options, the only peptide hormone among the choices is **Glucagon**.

### Final Answer:
**Glucagon is a peptide hormone.**