Which among the following statement is true about Schottky defect ?

Options

A. In the defect cation and anion are lacking in stoichiometric proportion.
B. Formation of metal alloy is example of this defect.
C. In this, regular cation is replaced by different cation
D. In this cation or anion moves from regular site to place between lattice site.

Explanation

To determine which statement is true about the Schottky defect, let's analyze the concept step by step.

### Step 1: Understand the Schottky Defect
The Schottky defect is a type of point defect in ionic crystals. It occurs when equal numbers of cations and anions are missing from their lattice sites, creating vacancies. This defect maintains the stoichiometry of the compound.

**Hint:** Recall that the Schottky defect involves the removal of both cations and anions from the lattice.

### Step 2: Analyze the Statements
1. **Statement 1:** In the defect, cation and anion are lacking in a stoichiometry.
- This statement is true because, in a Schottky defect, both cations and anions are missing in equal numbers, preserving the overall stoichiometric ratio of the compound.

2. **Statement 2:** Formation of metal alloy is an example of this effect.
- This statement is false. Schottky defects are specific to ionic solids and do not apply to metal alloys.

3. **Statement 3:** In this, a regular cation is replaced by a different cation.
- This statement is false. This describes a different type of defect known as a Frenkel defect, not a Schottky defect.

4. **Statement 4:** In this, cation and anion move from regular site to places between the lattice site.
- This statement is also false. In a Schottky defect, cations and anions are simply missing from their lattice sites rather than moving to different positions.

### Step 3: Conclusion
Based on the analysis of the statements, the only true statement regarding the Schottky defect is:
- **Statement 1:** In the defect, cation and anion are lacking in a stoichiometry.

**Final Answer:** The true statement about the Schottky defect is that cation and anion are lacking in a stoichiometric ratio.