Curie temperature refers to the temperature at which a material undergoes a phase transition from a paramagnetic phase to a ferromagnetic phase. In the case of iron, the Curie temperature is 770 degrees Celsius.

- Paramagnetic and Ferromagnetic Phases:
- In a paramagnetic phase, the magnetic moments of individual atoms or ions align randomly, resulting in a net magnetization of zero.
- In a ferromagnetic phase, the magnetic moments of atoms or ions align in a parallel manner, resulting in a net magnetization.

- Explanation of the Correct Answer (option 'C'):
- The Curie temperature of iron is 770 degrees Celsius. This means that below this temperature, iron exhibits ferromagnetic behavior, and above this temperature, it becomes paramagnetic.
- At temperatures below the Curie temperature, the magnetic moments of iron atoms align in a parallel manner, resulting in a strong net magnetization.
- As the temperature increases above the Curie temperature, the thermal energy disrupts the alignment of magnetic moments, causing a decrease in net magnetization.
- When iron is heated above its Curie temperature, it loses its ferromagnetic properties and becomes paramagnetic, where the magnetic moments align randomly.

- Other Options:
- Option 'A': 200 degrees Celsius is incorrect because it is much lower than the actual Curie temperature of iron.
- Option 'B': 430 degrees Celsius is incorrect because it is also lower than the actual Curie temperature of iron.
- Option 'D': 550 degrees Celsius is incorrect because it is lower than the actual Curie temperature of iron.

In conclusion, the correct answer is option 'C' as the Curie temperature of iron is 770 degrees Celsius.