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Which among the following statements about crystal structures are correct? (Choose all that apply.) (A) In a caesium chloride crystal, the coordination number of each type of ion is 8. (B) A metal crystallising in a body-centred cubic arrangement has a coordination number of 12. (C) In an ionic crystal, each unit cell shares certain ions with neighbouring unit cells. (D) Given that the ionic radii of Na+ and Cl- are 95 pm and 181 pm respectively, the edge length of the NaCl unit cell is 552 pm.

1. A and C are correct
2. A, C, and D are correct
3. B and D are correct
4. Only C is correct

Correct answer: A, C, and D are correct

Solution

Statement A is correct (CsCl structure: CN = 8 for both ions). Statement B is incorrect (BCC has CN = 8, not 12; FCC/HCP have CN = 12). Statement C is correct (corner ions are shared among 8 unit cells, etc.). Statement D is correct (2*(95+181) = 552 pm).

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