Which of the following statements is/are correct?

Options

A. If three `Fe^(2+)` ions are missing from their lattice in`FeO`, then there must be two `Fe^(3+)` ions somewhere in the lacttice.
B. Crystals with matal deficiency defects are called super conductors.
C. Crystals with metal deficiency are called semiconductors.
D. `1` Bohr Magneton `= 9.27 xx 10^(-24) A m^(2)`

Answer

To determine which statements are correct, we will analyze each statement one by one based on the principles of solid-state chemistry.

### Step-by-Step Solution:

1. **Statement A**: "If three Fe²⁺ ions are missing from their lattice in FeO, then there must be two Fe³⁺ ions somewhere in the lattice."
- **Analysis**: FeO is a neutral compound. If three Fe²⁺ ions are missing, this creates a deficiency of +6 charge (since each Fe²⁺ contributes +2 charge). To maintain electrical neutrality, there must be an equivalent positive charge present. Therefore, the presence of two Fe³⁺ ions (+3 charge each) will compensate for the missing charge (+2 * 3 = +6).
- **Conclusion**: This statement is **correct**.

2. **Statement B**: "Crystals with metal deficiency defects are called superconductors."
- **Analysis**: Superconductors are materials that exhibit zero electrical resistance and expulsion of magnetic fields at very low temperatures. They do not necessarily have metal deficiency defects. Instead, they are characterized by their ability to conduct electricity without resistance, which is a different property from metal deficiency.
- **Conclusion**: This statement is **incorrect**.

3. **Statement C**: "Crystals with metal deficiencies are called semiconductors."
- **Analysis**: Semiconductors do exhibit metal deficiency defects, which contribute to their electrical properties. These defects allow semiconductors to conduct electricity better than insulators but not as well as conductors. The presence of these defects is crucial for their function in electronic devices.
- **Conclusion**: This statement is **correct**.

4. **Statement D**: "One Bohr magneton is 9.27 x 10⁻²⁴ A·m²."
- **Analysis**: The Bohr magneton is indeed a physical constant used to describe the magnetic moment of an electron due to its orbital or spin angular momentum. The value given in the statement is accurate.
- **Conclusion**: This statement is **correct**.

### Final Conclusion:
The correct statements are A, C, and D. Statement B is incorrect.