For the metamorphosis of tadpoles which of the following elements must be available in water?

Options

A. chlorine
B. carbon
C. sulphur
D. iodine

Answer

**Step-by-Step Solution:**

1. **Understanding Metamorphosis**: Metamorphosis is a biological process where an animal undergoes physical development after birth or hatching. For tadpoles, this process transforms them into adult frogs.

2. **Identifying the Elements**: The question asks which element must be available in water for the metamorphosis of tadpoles. We need to evaluate the given options: Chlorine, Carbon, Sulphur, and Iodine.

3. **Evaluating Each Option**:
- **Chlorine**: This element is harmful to tadpoles and can kill them, so it cannot be necessary for their metamorphosis.
- **Carbon**: While carbon is essential for life, it does not play a direct role in the metamorphosis process of tadpoles.
- **Sulphur**: Sulphur is not involved in the metamorphosis of tadpoles, so this option is also incorrect.
- **Iodine**: This element is crucial because it is necessary for the production of the thyroxine hormone, which regulates the metamorphosis process in tadpoles.

4. **Conclusion**: Based on the evaluation, the correct answer is **Iodine**. It is essential for the release of thyroxine from the thyroid gland, which is necessary for the metamorphosis of tadpoles.

**Final Answer**: Iodine must be available in water for the metamorphosis of tadpoles.

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