Which of the following represents the hexagonal close-packed $(HCP)$ arrangement of spheres?

Atom $(A)$ is present in $ccp$ form,atom $(B)$ is present in all the octahedral voids,and atom $(C)$ is present in all the tetrahedral voids. If all particles touching one of the body diagonal axes are removed,find the empirical formula of the solid.

In a solid $AB_2$,the coordination number of $A$ is $8$. It has a cubic close-packed $(ccp)$ lattice. Half of the $B$ atoms are,however,ejected from the solid. Now,the number of tetrahedral holes (voids) that remain filled is:

$A$ body-centred cubic $(BCC)$ lattice is made up of two different types of atoms $X$ and $Y$. Atom $X$ occupies the body centre and atoms $Y$ occupy the corner positions. One of the corners is left unoccupied per unit cell. The empirical formula of it is

Find the number of tetrahedral voids per atom in a crystal lattice.

In a face-centered cubic $(FCC)$ unit cell (or cubic close packing $(CCP)$ unit cell),the edge length $a$ is equal to: