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Which of the following statements is/are...

Which of the following statements is/are correct about hexagonal close packing ?
1. The coordination number is 8
2. It is ABAB type packing in which third layer is aligned with the first layer
3. Be, Mg, Mo etc. are found to have hcp structure
4. In hcp, atoms occupy 74% of the available space

A

2,3

B

3,4

C

2,3,4

D

1,2,3

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question regarding the statements about hexagonal close packing (hcp), we will analyze each statement one by one. ### Step-by-Step Solution: 1. **Statement 1: The coordination number is 8.** - In hexagonal close packing, each atom is surrounded by 12 other atoms. This includes 6 atoms in the same layer and 3 atoms in the layer above and 3 atoms in the layer below. Therefore, the coordination number is 12, not 8. - **Conclusion**: This statement is **incorrect**. 2. **Statement 2: It is ABAB type packing in which the third layer is aligned with the first layer.** - Hexagonal close packing is indeed characterized by an ABAB arrangement. In this arrangement, the third layer is aligned with the first layer. This is a defining feature of hcp. - **Conclusion**: This statement is **correct**. 3. **Statement 3: Be, Mg, Mo, etc. are found to have hcp structure.** - Elements such as beryllium (Be), magnesium (Mg), and molybdenum (Mo) do exhibit hexagonal close packing structures in their solid forms. - **Conclusion**: This statement is **correct**. 4. **Statement 4: In hcp, atoms occupy 74% of the available space.** - The packing efficiency of hexagonal close packing is indeed 74%, meaning that 74% of the volume is occupied by the atoms, while the remaining 26% is empty space. - **Conclusion**: This statement is **correct**. ### Final Conclusion: - The correct statements about hexagonal close packing are **2, 3, and 4**. The incorrect statement is **1**. ### Summary of Correct Statements: - **Correct**: 2, 3, 4 - **Incorrect**: 1
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