Which of the following statements are correct? 

• A

  A NaCl type is f.c.c. unit cells with corners and faces occupied by either cation or anion

• B

  In a face-centred cubic unit cell, the body centre is an octahedral void 

• C

  In f. c. c. unit cell, octahedral and tetrahedral voids are equal

• D

  Tetrahedral voids = 2 × octahedral voids, is true for only c. c. p and h. c. p.