What is the coordination number of a particle in an $fcc$ crystal lattice?

How many nearest neighbours are there for $Si$ and $O$ atoms in quartz crystals?

$A$ compound made of elements $A$ and $B$ forms an $fcc$ structure. Atoms of $A$ are at the corners and atoms of $B$ are present at the centres of the faces of the cube. What is the formula of the compound?

The radius of $Na^{+}$ is $95 \, pm$ and the radius of $Cl^{-}$ ion is $181 \, pm$. What is the coordination number of $Na^{+}$?

The number of equidistant oppositely charged ions in a sodium chloride crystal is

For an ionic crystal of the type $AB$,the value of the limiting radius ratio is $0.40$. This value suggests that the crystal structure should be: