Statement - I. Due to Frenkel defect the density of solid decrease. Statement - II. In frenkel defect cation or anion is present at interstitial site leaving lattice sites vacant.

Options

A. If both Statement- I and Statement- II are true, and Statement - II is the correct explanation of Statement– I.
B. If both Statement - I and Statement - II are true but Statement - II is not the correct explanation of Statement – I.
C. If Statement - I is true but Statement - II is false.
D. If Statement - I is false but Statement - II is true.

Answer

To analyze the statements regarding Frenkel defect, let's break down the concepts step by step.

### Step 1: Understand Frenkel Defect
Frenkel defect is a type of point defect in a crystal lattice where an atom or ion (usually a cation) is displaced from its normal lattice position to an interstitial site, creating a vacancy at the original lattice site.

**Hint:** Remember that in a Frenkel defect, an atom moves to a position where it is not normally found, creating a vacancy.

### Step 2: Analyze Statement I
**Statement I:** "Due to Frenkel defect the density of solid decreases."

To determine if this statement is true or false, we need to consider how density is defined:
- Density (ρ) = Mass (m) / Volume (V)

In the case of a Frenkel defect:
- The total mass of the solid remains unchanged because no atoms leave the crystal; they simply move from one position to another.
- The volume of the unit cell remains constant as the same number of atoms are present in the lattice.

Since both mass and volume remain constant, the density does not change. Therefore, Statement I is **false**.

**Hint:** Consider how mass and volume are affected by the movement of atoms in the lattice.

### Step 3: Analyze Statement II
**Statement II:** "In Frenkel defect cation or anion is present at interstitial site leaving lattice sites vacant."

This statement accurately describes the Frenkel defect. In this defect, a cation (or sometimes an anion) occupies an interstitial site, which results in a vacancy at the lattice site from which it moved. Thus, Statement II is **true**.

**Hint:** Recall the definition of Frenkel defect and what happens to the cations and anions.

### Conclusion
- **Statement I** is **false**: The density of solid does not decrease due to Frenkel defect.
- **Statement II** is **true**: It correctly describes the nature of the Frenkel defect.

### Final Answer
- Statement I: False
- Statement II: True