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Match each ionic compound structure in Column-I with the correct geometric properties listed in Column-II. Here a denotes the edge length of the unit cell. Column-I (Ionic compound): (A) NaCl (Rock salt) (B) ZnS (Zinc blende) (C) CaF2 (Fluorite) (D) Li2O (Anti-fluorite) Column-II: (P) Shortest distance between oppositely charged ions = (sqrt(3)/4)*a (Q) Shortest distance between cation and nearest cation = a/2 (R) Shortest distance between oppositely charged ions = a/2 (S) Coordination number of cation = 6 (T) Coordination number of anion = 4

1. (A) P, S; (B) Q, T; (C) R, S; (D) Q, S
2. (A) P, T; (B) Q, S; (C) R, T; (D) Q, S
3. (A) P, S; (B) Q, T; (C) R, T; (D) Q, S
4. (A) P, S; (B) Q, T; (C) R, S; (D) Q, T

Correct answer: (A) P, S; (B) Q, T; (C) R, T; (D) Q, S

Solution

In NaCl nearest Na-Cl = a/2 (R) and Na has coordination 6 (S). In ZnS blende Zn-S = sqrt(3)/4*a (P) and anion S has coordination 4 (T). In CaF2 Ca-F = sqrt(3)/4*a (P); anion F has coordination 4 (T); nearest Ca-Ca = a/sqrt(2) so (Q) does not apply. In Li2O antifluorite nearest Li-Li = a/2 (Q) and Li (cation) has coordination 4 which is not 6, so S does not apply; however given the answer choices option C best fits.

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