Assertion : The packing efficiency is maximum for the fcc structure.
Reason : The cordination number is 12 in fcc structure.

Options

A. Assertion and reason both are corrent statements and reason is correct explanation for assertion.
B. Assertion and reason both are corrent statements but reason is not correct explanation for assertion.
C. Assertion is corrent statement but reason reason is wrong statement.
D. Assertion is wrong statement but reason is correct statement.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "The packing efficiency is maximum for the FCC structure."
- In solid-state chemistry, packing efficiency refers to the fraction of volume in a crystal structure that is occupied by the constituent particles (atoms, ions, or molecules).

2. **Calculating Packing Efficiency**:
- For different types of unit cells, the packing efficiencies are as follows:
- Simple Cubic (SC): 52.33%
- Body-Centered Cubic (BCC): 68%
- Face-Centered Cubic (FCC): 74%
- From these values, we can conclude that the FCC structure indeed has the highest packing efficiency among the three types of cubic structures.

3. **Understanding the Reason**:
- The reason states that "The coordination number is 12 in FCC structure."
- The coordination number refers to the number of nearest neighbors surrounding a particular atom in the crystal lattice.
- In the FCC structure, each atom is surrounded by 12 other atoms, which is correct.

4. **Analyzing the Relationship**:
- While both the assertion and reason are correct statements, they are independent of each other. The packing efficiency being maximum does not directly depend on the coordination number being 12.
- Therefore, the reason does not correctly explain the assertion.

5. **Conclusion**:
- Since both the assertion and reason are correct but the reason does not explain the assertion, the correct answer is that both statements are correct but the reason is not the correct explanation for the assertion.

### Final Answer:
The correct option is: **Assertion and reason both are correct statements but reason is not the correct explanation for assertion.**

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