Thyroxine acts on every organ except
(a) Brain
(b) Testis
(c) Thyroid
(d) All the above

Options

A. Brain
B. Testis
C. Thyroid
D. All the above.

Answer

To solve the question "Thyroxine acts on every organ except," we will analyze the options provided and understand the role of thyroxine in the body.

### Step-by-Step Solution:

1. **Understanding Thyroxine**:
- Thyroxine (T4) is a hormone produced by the thyroid gland. It plays a crucial role in regulating metabolism, growth, and development in the body.

2. **Analyzing the Options**:
- **Option (a) Brain**: Thyroxine does act on the brain. It is essential for brain development and function.
- **Option (b) Testis**: Thyroxine also acts on the testis, influencing male reproductive functions and development.
- **Option (c) Thyroid**: The thyroid gland produces thyroxine; therefore, it does not act on itself as a target organ.
- **Option (d) All the above**: This option suggests that thyroxine does not act on any of the listed organs, which is incorrect based on the analysis of the previous options.

3. **Conclusion**:
- Since thyroxine does not act on the thyroid gland itself (as it is the organ producing it), the correct answer is **(c) Thyroid**.

### Final Answer:
(c) Thyroid

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