vi. Which of the following is not correct?
a. Four spheres are involved in the formation of tetrahedral void.
b. The centres of spheres in octahedral voids are at the apices of a regular tetrahedron.
c. If the number of atoms is N the number of octahedral voids is 2N.
d. If the number of atoms is N/2, the number of tetrahedral voids is N.