There are three cubic unit cells A, B and C. A is FCC and all of its tetrahedral voids are also occu — Solid State Chemistry Question
Question
There are three cubic unit cells A, B and C. A is FCC and all of its tetrahedral voids are also occupied. B is also FCC and all of its octahedral voids are also occupied. C is simple cubic and all of its cubic voids are also occupied. If voids in all unit cells are occupied by the spheres exactly at their limiting radius, then the order of packing efficiency would be
Answer: B
💡 Solution & Explanation
Packing efficiency (PE) calculations: For C (simple cubic + cubic void), $PE \approx 0.728$. For A (FCC + tetrahedral voids), $PE \approx 0.74 \times (1 + 2(0.225)^3) \approx 0.756$. For B (FCC + octahedral voids), $PE \approx 0.74 \times (1 + (0.414)^3) \approx 0.792$. The order is C < A < B. Therefore, correct answer is B.
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