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
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