Which of the following statements is not about the voids ?

Options

A. Octahedral void is formed at the centre of six spheres which lies at the apices of a regular octahedron
B. There is one octahedral site for each sphere
C. There are two tetrahedral sites for each sphere
D. Octahedral voids are formed when the triangular voids in second layer exactly overlap with similar voids in the first layer .

Explanation

To determine which statement is not about the voids, let's analyze each option step by step.

### Step 1: Analyze the First Statement
**Statement:** "Octahedral voids are formed at the center of six spheres which lie at the vertices of a regular octahedron."

- **Analysis:** This statement is correct. An octahedral void is indeed located at the center of six spheres arranged at the vertices of a regular octahedron.

### Step 2: Analyze the Second Statement
**Statement:** "There is one octahedral void for each sphere."

- **Analysis:** This statement is also correct. In a close-packed arrangement, each sphere contributes one octahedral void.

### Step 3: Analyze the Third Statement
**Statement:** "There are two tetrahedral voids for each sphere."

- **Analysis:** This statement is correct as well. In a close-packed structure, each sphere does indeed have two tetrahedral voids associated with it.

### Step 4: Analyze the Fourth Statement
**Statement:** "Octahedral voids are formed when the triangular void in the second layer exactly overlaps with the similar void in the first layer."

- **Analysis:** This statement is incorrect. Octahedral voids are formed when three close-packed spheres are arranged in a triangular formation, and another set of three spheres is placed above them in a specific orientation, not by overlapping triangular voids.

### Conclusion
Based on the analysis, the statement that is not about the voids is:
**D: "Octahedral voids are formed when triangular void in the second layer exactly overlap with similar void in the first layer."**

### Final Answer
**The correct answer is D.**

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