When anion leaves the normal lattice site and electron occupies interstitial sites in its crystal lattice, It is called:

Options

A. Schottky defect
B. Frenkel defect
C. Metal excess defect
D. Stoichiometric defect

Answer

To solve the question, we need to identify the type of defect that occurs when an anion leaves its normal lattice site and an electron occupies an interstitial site in a crystal lattice. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Lattice Structure
In a typical ionic crystal lattice, such as NaCl, there are alternating cations (Na⁺) and anions (Cl⁻) arranged in a specific pattern. Each ion occupies a defined lattice site.

**Hint:** Remember that in ionic crystals, cations and anions are arranged in a regular pattern to maintain electrical neutrality.

### Step 2: Identify the Movement of Ions
The question states that an anion (like Cl⁻) leaves its normal lattice site. This creates a vacancy in the lattice where the anion used to be.

**Hint:** Think about what happens to the overall charge balance when an ion leaves its site.

### Step 3: Consider the Role of the Electron
When the anion leaves, an electron occupies an interstitial site (a space between the lattice sites). This electron is negatively charged and can help maintain electrical neutrality because it replaces the negative charge of the missing anion.

**Hint:** Consider how the presence of an electron affects the charge balance in the lattice.

### Step 4: Identify the Type of Defect
This situation describes a **metal excess defect**. In this type of defect, the absence of an anion leads to an excess of positive charge (from the cations), but the electron compensates for this by providing additional negative charge. Therefore, the overall charge balance is maintained, but there is an excess of metal ions.

**Hint:** Recall that a metal excess defect occurs when there is an imbalance created by missing anions, leading to an excess of cations.

### Step 5: Eliminate Other Options
- **Schottky Defect:** Involves equal numbers of cations and anions missing, maintaining neutrality.
- **Frenkel Defect:** Involves a cation moving to an interstitial site, also maintaining neutrality.

Since neither of these options fits the scenario described in the question, we confirm that the correct answer is indeed the metal excess defect.

### Final Answer
When an anion leaves the normal lattice site and an electron occupies the interstitial site in its crystal lattice, it is called a **metal excess defect**.

---