Assertion: Crystalline solids are anisotropic.
Reason: Cystalline solids are not as closely packed as ionic solids.

Options

A. If both assertion and reason are correct and reason is correct explanation for assertion
B. If both assertion and reason are correct but reason is not correct explanation for assertion
C. If assertion is correct but reason is incorrect
D. If both assertion and reason are incorrect

Explanation

To solve the question, we will analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states that "Crystalline solids are anisotropic."

- **Definition of Anisotropic**: Anisotropic materials have properties that vary when measured in different directions.
- **Crystalline Solids**: These solids have a well-defined geometric structure and a regular arrangement of particles (atoms, ions, or molecules).

**Conclusion for Step 1**: The assertion is true because crystalline solids exhibit different physical properties (like electrical resistance and refractive index) when measured along different directions due to their ordered structure.

### Step 2: Analyze the Reason
The reason states that "Crystalline solids are not as closely packed as ionic solids."

- **Packing in Crystalline Solids**: Crystalline solids can be closely packed, depending on the type of solid (metallic, ionic, covalent, etc.).
- **Ionic Solids**: These are a type of crystalline solid where ions are arranged in a lattice structure. They can also be closely packed, but this does not mean that all crystalline solids are less densely packed than ionic solids.

**Conclusion for Step 2**: The reason is false because crystalline solids can be closely packed, and the anisotropic nature of crystalline solids arises from the arrangement of particles, not from their packing density compared to ionic solids.

### Final Conclusion
- The assertion is true: Crystalline solids are indeed anisotropic.
- The reason is false: Crystalline solids can be closely packed, and their anisotropy is due to particle arrangement, not packing density.

Thus, the correct answer is that the assertion is true, but the reason is false.