Question

Which of the following is not an allotropic form of iron?

• A. \( \alpha \)
• B. \( \rho \)
• C. \( \gamma \)
• D. \( \theta \)

Hint:

Iron exists in different allotropic forms: \( \alpha \) (Ferrite), \( \gamma \) (Austenite), and \( \delta \) (High-temperature BCC). These influence steel properties.

Answer 1

The Correct Option is B

Iron exhibits different allotropes based on temperature, affecting its crystal structure and properties.
Step 1: Understanding the Allotropic Forms of Iron - \( \alpha \)-Iron (Ferrite): Stable at room temperature, BCC structure. - \( \gamma \)-Iron (Austenite): Stable between 912°C and 1394°C, FCC structure. - \( \delta \)-Iron: Stable between 1394°C and 1538°C, BCC structure.


Step 2: Evaluating the Options - Option (A) - Incorrect: \( \alpha \)-Iron (Ferrite) is an allotropic form of iron.
- Option (B) - Correct: \( \rho \) is not an allotropic form of iron.
- Option (C) - Incorrect: \( \gamma \)-Iron (Austenite) is a stable form of iron at high temperatures.
- Option (D) - Incorrect: \( \theta \) represents iron carbide (Fe\(_3\)C), which is a compound, not an allotrope.


Step 3: Conclusion Since \( \rho \) is not an allotropic form of iron, the correct answer is option (B).