A : In Schottky defect, density of crystal decreases.
R : Equal number of cations and anions are missing in Schottky defect.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To analyze the given statements regarding Schottky defects, we will break down the assertion (A) and reason (R) step by step.

### Step-by-Step Solution:

1. **Understanding Schottky Defect**:
- A Schottky defect is a type of point defect in a crystal lattice where an equal number of cations and anions are missing from their lattice sites. This defect maintains the stoichiometry of the compound.

2. **Assertion Analysis (A)**:
- The assertion states that "In Schottky defect, density of crystal decreases."
- When cations and anions are missing, the overall mass of the crystal decreases while the volume remains the same. Since density is defined as mass per unit volume (Density = Mass/Volume), a decrease in mass while volume remains constant results in a decrease in density.

3. **Reason Analysis (R)**:
- The reason states that "Equal number of cations and anions are missing in Schottky defect."
- This statement is true. In a Schottky defect, the loss of cations and anions occurs in equal numbers to maintain the overall charge neutrality of the crystal.

4. **Conclusion**:
- Both the assertion (A) and the reason (R) are true. The assertion correctly describes the effect of Schottky defects on crystal density, and the reason accurately explains the nature of the defect.

### Final Answer:
- Both A and R are true, and R is the correct explanation of A.

---