Which of the following statements is /are not true?

Options

A. Density of solid gets increased due to interstitial defects
B. Frenkel defects do not alter the density of the solid
C. Non - stoichiometric defects modify the formula of the compound
D. Non - stoichiometric defects do not alter the density of the solid

Answer

To determine which of the statements about defects in solids are not true, we will analyze each statement step by step.

### Step 1: Analyze the First Statement
**Statement:** The density of solids gets increased due to interstitial defect.

**Explanation:** Interstitial defects occur when extra atoms are inserted into the interstitial spaces of a crystal lattice. This addition of atoms increases the mass of the solid without significantly increasing its volume, leading to an increase in density.

**Conclusion:** This statement is **true**.

### Step 2: Analyze the Second Statement
**Statement:** Frenkel defects do not alter the density of the solid.

**Explanation:** In a Frenkel defect, an ion leaves its lattice site and occupies an interstitial site. Although the arrangement of ions changes, the total number of ions remains the same. Therefore, the mass and volume of the solid do not change, and the density remains constant.

**Conclusion:** This statement is **true**.

### Step 3: Analyze the Third Statement
**Statement:** Non-stoichiometric defects modify the formula of the compound.

**Explanation:** Non-stoichiometric defects occur when the ratio of cations to anions in a compound deviates from the ideal stoichiometric ratio. This change in ratio can lead to a modification of the empirical formula of the compound.

**Conclusion:** This statement is **true**.

### Step 4: Analyze the Fourth Statement
**Statement:** Non-stoichiometric defects do not alter the density of the solid.

**Explanation:** Non-stoichiometric defects involve a variation in the composition of the solid, which can lead to changes in the density. As the composition varies, the density can also change due to the differing amounts of cations and anions.

**Conclusion:** This statement is **not true**.

### Final Conclusion
The statements that are **not true** are:
- The fourth statement: "Non-stoichiometric defects do not alter the density of the solid."

### Summary of Findings
- **True Statements:**
1. Density of solids gets increased due to interstitial defect.
2. Frenkel defects do not alter the density of the solid.
3. Non-stoichiometric defects modify the formula of the compound.
- **Not True Statement:**
4. Non-stoichiometric defects do not alter the density of the solid.