Which set of characteristics of ZnS crystal is correct

a. Coordination number ( 4 : 4); ccp;  Zn⁺⁺   ion in the alternate tetrahedral voids

b. Coordination number ( 6 : 6); hcp;  Zn⁺⁺   ion in the alternate tetrahedral voids

c. Coordination number ( 6 : 4); hcp;  Zn⁺⁺   ion in the alternate octahedral  voids

d. Coordination number ( 4 : 4); ccp;  Zn⁺⁺   ion in the alternate tetrahedral voids

Ans. a

Explanation : ZnS has zinc blende structure. It has cubic close packed structure. The S ^2- ions are present at the corners of the cube and the cube and at the centre of each face. Zinc ions occupy half of the tetrahedral sites. Each zinc ion is surrounded by four sulphide ions which are disposed towards the corners of a regular tetrahedron. Similarly S^2-  ion is surrounded by four Zn²⁺  ions.