Which one is unrelated?

Options

A. Ca - muscle contraction
B. I - thyroid
C. Co - energy liberation
D. Cl - nerve conduction

Answer

To solve the question "Which one is unrelated?", we need to analyze the four options provided and their corresponding functions.

### Step-by-Step Solution:

1. **Identify the first option: Calcium and Muscle Contraction**
- Calcium ions play a crucial role in muscle contraction. They are stored in the sarcoplasm of muscle cells and are released upon stimulation. When released, calcium binds to the troponin complex, which initiates the contraction process.
- **Conclusion**: This option is related.

2. **Identify the second option: Iodine and Thyroid**
- Iodine is an essential component of the hormone thyroxin, which is produced by the thyroid gland. Thyroxin is critical for regulating metabolism and growth.
- **Conclusion**: This option is related.

3. **Identify the third option: Cobalt and Energy Liberation**
- Cobalt is a component of vitamin B12, which is involved in various metabolic processes, including the Krebs cycle. The Krebs cycle is essential for ATP production, which is the energy currency of the cell.
- **Conclusion**: This option is related.

4. **Identify the fourth option: Chloride and Nerve Conduction**
- Nerve conduction primarily involves sodium (Na+) and potassium (K+) ions. While chloride ions (Cl-) do play a role in maintaining the resting membrane potential and overall ionic balance, they are not directly responsible for the conduction of nerve impulses.
- **Conclusion**: This option is unrelated.

### Final Answer:
The option that is unrelated is **option number 4: Chloride for nerve conduction**.

---