Thyroxine is

Options

A. Follicles of thyroid gland
B. Stored in follicle cells of thyroid
C. Inactive form of triiodothyroine
D. Stored in pituitary gland .

Answer

**Step-by-Step Solution:**

1. **Identify the Source of Thyroxine**: Thyroxine, also known as T4, is a hormone secreted by the thyroid gland. It is produced in the follicular cells of the thyroid.

2. **Understand the Structure of Thyroxine**: Thyroxine is chemically known as tetraiodothyronine (T4) because it contains four iodine atoms in its structure.

3. **Function of Thyroxine**: The primary role of thyroxine is to regulate metabolic activities in the body. It increases the consumption of oxygen in metabolically active tissues, thereby influencing overall metabolism.

4. **Conversion to Active Form**: Thyroxine (T4) is converted into its more active form, triiodothyronine (T3), primarily in the liver and kidneys. T3 is considered more biologically active than T4.

5. **Conclusion**: Based on the information provided, thyroxine (T4) can be considered as an inactive form of triiodothyronine (T3) since T3 is the active hormone that exerts the metabolic effects.

6. **Final Answer**: Therefore, the correct answer to the question "Thyroxine is" is that it is the inactive form of triiodothyronine.

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