Following are the functions of a particular hormone:
(a) controller of circadian rhythm in humans
(b) helps in pigmentation, metabolism, menstrual cycle
(C ) controls the defence mechanism of the body
Name the hormone.

Options

A. Epinephrine
B. Gastrin
C. Melatonin
D. Insulin.

Answer

To solve the question regarding the hormone with the specified functions, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Functions Listed**: The question provides three specific functions of a hormone:
- Controller of circadian rhythm in humans
- Helps in pigmentation, metabolism, menstrual cycle
- Controls the defense mechanism of the body

2. **Analyze Each Hormone Option**:
- **Epinephrine**: This hormone is primarily known as an emergency hormone produced by the adrenal medulla. It mainly increases heart rate and respiration but does not control circadian rhythms or the menstrual cycle. Hence, it is not the correct answer.

- **Gastrin**: This hormone stimulates gastric glands to secrete hydrochloric acid and pepsinogen. It is involved in digestion but does not relate to circadian rhythms, pigmentation, or the defense mechanism. Therefore, it is also not the correct answer.

- **Melatonin**: This hormone is produced by the pineal gland and is crucial for regulating the sleep-wake cycle (circadian rhythm). It also influences pigmentation, metabolism, and the menstrual cycle, and has roles in the immune response. This aligns with all the functions mentioned in the question.

- **Insulin**: This hormone is produced by the pancreas and primarily regulates blood glucose levels. It does not have a role in circadian rhythms, pigmentation, or the menstrual cycle. Thus, it is not the correct answer.

3. **Conclusion**: Based on the analysis, the hormone that fits all the described functions is **Melatonin**.

### Final Answer:
The hormone is **Melatonin**.

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