In a close-packed lattice,the number of tetrahedral voids compared to the number of octahedral voids is:

Which of the following statements is correct for an $fcc$ lattice?

$A$ compound formed by $Mg$,$Al$,and $O$ is found to have a cubic close-packed $(CCP)$ array of oxide ions,in which $Mg^{2+}$ ions occupy $\frac{1}{8}^{th}$ of the tetrahedral voids and $Al^{3+}$ ions occupy $\frac{1}{2}$ of the octahedral voids. The formula for the compound is:

Which of the following is not a close-packed structure?

Ferric oxide crystallises in a hexagonal close-packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.

Atoms of an element $Z$ form a hexagonal closed packed $(hcp)$ lattice and atoms of element $X$ occupy all the tetrahedral voids. The formula of the compound is