No crystal is found to be prefect at room temperature. The defects present in the crystals can be stoichimetric or non-stoichiometric. Due to non-stoichimetric defects, the formula of the ionic compound is different from the ideal formula. For example , the ideal formula of ferrous oxide should be FeO but actually in one sample , it was found to be ` Fe_(0.93)`O. This is because the crystal may have some ferric ions in place of ferrous ions. These defects change the propeties of the crystals. In some cases, defects are introduced to have crystals of desired properties as required in the field of electronics. Doping of elments of Group 14 with those of Group 13 or 15 is most common. In ionic compounds, usually impurities are introduced in which the cation has higher valency than the cation of the parent crystal, e.g, ` SrCl_(2)` into NaCl.
which one of the following defects does not affect the density of the crystal ?

Options

A. Schottky defect
B. Interstitial defect
C. Frenkel defect
D. Both in (b) and (c )

Explanation

To solve the question regarding which defect does not affect the density of the crystal, we will analyze the different types of defects mentioned in the video transcript. Here’s a step-by-step solution:

### Step 1: Understand the Types of Defects
Defects in crystals can be classified into two main categories: stoichiometric and non-stoichiometric defects. We need to focus on the types of defects and their effects on density.

### Step 2: Identify the Defects
1. **Schottky Defect**: This defect involves the absence of an equal number of cations and anions from the crystal lattice. This results in a decrease in density because there are fewer ions in the lattice.

2. **Interstitial Defect**: In this defect, extra atoms (usually of a different element) occupy the interstitial spaces in the crystal lattice. This increases the density because there are more atoms present in the structure.

3. **Frenkel Defect**: This defect occurs when a cation leaves its original position and occupies an interstitial site. The overall number of ions remains the same, so the density does not change.

### Step 3: Analyze the Effects on Density
- **Schottky Defect**: Decreases density.
- **Interstitial Defect**: Increases density.
- **Frenkel Defect**: Density remains the same.

### Step 4: Conclusion
From the analysis, we can conclude that the **Frenkel defect** does not affect the density of the crystal.

### Final Answer
The defect that does not affect the density of the crystal is the **Frenkel defect**.

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