Which of the following will have metal deficiency defect?

Options

A. NaCl
B. FeO
C. KC
D. ZnO

Answer

To determine which compound exhibits a metal deficiency defect, we need to understand the concept of metal deficiency defects in ionic crystals.

### Step-by-Step Solution:

1. **Understanding Metal Deficiency Defect**:
- A metal deficiency defect occurs when there is a vacant lattice site due to a missing cation (metal ion). This defect is characterized by the presence of fewer cations than anions in the crystal lattice.

2. **Charge Compensation**:
- To maintain electrical neutrality in the crystal, one of the neighboring metal ions may take on an extra positive charge. This is essential because the absence of a cation creates a positive charge imbalance.

3. **Variable Valency**:
- Metal deficiency defects are typically found in compounds where the metal can exhibit variable valency. Transition metals are known for their ability to exist in multiple oxidation states, making them candidates for this type of defect.

4. **Analyzing the Given Options**:
- We need to evaluate the options provided to see which one contains a metal that can exhibit variable valency:
- **Option 1: NaCl** - Sodium (Na) has a fixed valency of +1 and does not exhibit variable valency. Thus, it does not show a metal deficiency defect.
- **Option 2: FeO** - Iron (Fe) can exhibit variable valency (Fe²⁺ and Fe³⁺). Therefore, it can show a metal deficiency defect.
- **Option 3: KCl** - Potassium (K) has a fixed valency of +1 and does not exhibit variable valency. Thus, it does not show a metal deficiency defect.
- **Option 4: ZnO** - Zinc (Zn) typically exhibits a fixed valency of +2 and does not show variable valency. Therefore, it does not show a metal deficiency defect.

5. **Conclusion**:
- Among the given options, only **FeO** (Option 2) can exhibit a metal deficiency defect due to the variable valency of iron.

### Final Answer:
The compound that will have a metal deficiency defect is **FeO** (Option 2).

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