Question:
Which of the following is not correct about the hexagonal close packing?
Which of the following is not correct about the hexagonal close packing?
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Remember HCP = ABAB stacking, while CCP/FCC = ABCABC stacking.
Updated On: Jun 9, 2026
- The co-ordination number is 12
- Packing efficiency in it is 74%
- Tetrahedral voids of the second layer are covered by the spheres of the third layer
- In this arrangement, spheres of the fourth layer are aligned with those of the first layer
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The Correct Option is C
Solution and Explanation
Concept:
Hexagonal close packing (HCP) follows an ABAB type stacking pattern.
Step 1: Analyze the stacking patterns of HCP.
In HCP: 1. Coordination number is 12. (Correct) 2. Packing efficiency is 74%. (Correct) 3. In HCP, the third layer covers the octahedral voids, not the tetrahedral voids. Tetrahedral voids are covered by the third layer in FCC/CCP (ABCABC type). (Incorrect) 4. The fourth layer is aligned with the first layer (ABAB stacking). (Correct)
Step 2: Conclude the incorrect statement.
Statement (C) claims tetrahedral voids are covered by the third layer, which is a characteristic of cubic close packing (CCP), not HCP. \[ \boxed{\text{Tetrahedral voids of the second layer are covered by the spheres of the third layer}} \]
Step 1: Analyze the stacking patterns of HCP.
In HCP: 1. Coordination number is 12. (Correct) 2. Packing efficiency is 74%. (Correct) 3. In HCP, the third layer covers the octahedral voids, not the tetrahedral voids. Tetrahedral voids are covered by the third layer in FCC/CCP (ABCABC type). (Incorrect) 4. The fourth layer is aligned with the first layer (ABAB stacking). (Correct)
Step 2: Conclude the incorrect statement.
Statement (C) claims tetrahedral voids are covered by the third layer, which is a characteristic of cubic close packing (CCP), not HCP. \[ \boxed{\text{Tetrahedral voids of the second layer are covered by the spheres of the third layer}} \]
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