In the Bragg's equation for diffraction of $X$-rays, $n$ represents:

An element $M$ crystallises in a body-centred cubic unit cell with a cell edge of $300 \, pm$. The density of the element is $6.0 \, g \, cm^{-3}$. The number of atoms present in $180 \, g$ of the element is $............ \times 10^{23}$ (Nearest integer).

Calculate the edge length of a unit cell for a metal with an atomic radius of $128 \ pm$ that forms an $fcc$ unit cell structure.

An ionic solid $X^{+} Y^{-}$ crystallizes in a $bcc$ structure. If the distance of the closest approach between the two ions is $173 \ pm$, what is the edge length of the unit cell in $pm$?

$A$ solid having density of $9 \times 10^3 \ kg \ m^{-3}$ forms face-centred cubic crystals of edge length $200 \sqrt{2} \ pm$. What is the molar mass of the solid? [Avogadro constant $\cong 6 \times 10^{23} \ mol^{-1}$,$\pi \cong 3$]

Metallic silver has $fcc$ structure. If the radius of the $Ag$ atom is $144 \ pm$, what is the edge length of the unit cell?