The correct statement in the following is

a. The ionic crystal of AgBr has Schottky defect

b. The unit cell having crystal parameters a = b ≠ c, α = β = 90 º  γ = 120 º is hexagonal

c. In ionic compounds having Freanked defect the ration r ₊ / r _–  is high

d. The coordination  number of Na ⁺  ion in NaCl is 4

Ans. b

(10)