Compute the percentage void space per unit volume of unit cell in zinc-fluride structure. In zinc fluoride, anions occupy

fcc positions and half of the tetrahedral holes are occupied by cations.

Q. Assertion :An important feature of Fluorite structure is that cations being large in size occupy FCC lattice points whereas anions occupy all the tetrahedral voids giving the formula unit $A{B}_2$ (A: cation, B: anion). Reason: There are 6 cations and 12 anions per FCC unit cell of the Fluorite structure.

Q. In zinc blende structure, anions are arranged in ccp and cations are present in the tetrahedral voids and only half the tetrahedral voids are occupied.
If 'a' is the edge length of the unit cell, then for zinc blende structure the distance of closest approach between cation and anion is :

Q.

In which of the following structures coordination number for cations and anions in the packed structure will be same ?

(a) $C{l}^{-}$ ions form fcc lattice and $N{a}^{+}$ ions occupy all octahedral voids of the unit cell

(b) $C{a}^{2+}$ ions form fcc lattice and $F^{-}$ ions occupy all the eight tetrahedral voids of the unit cell

(c) $O^{2-}$ ions form fcc lattice and $N{a}^{+}$ ions occupy all the eight tetrahedral voids of

(d) $S^{2-}$ ions form fcc lattice and $Z{n}^{2+}$ ions go into alternate tetrahedral voids of the unit cell

Q. $O^{2-}$ ions are arranged in ccp in a spinel structure. $A^{2+}$ ions occupy one-eighth of tetrahedral voids and $B^{+}$ ions occupy half of octahedral voids. The void volume of unit cell is $0.11$. Find the value of positive ions $A$ in unit cell.