$NaCl$ has $4$ formula units per unit cell. If the edge length of the unit cell is $0.564 \, nm$,then the density of the crystal is ............ $\text{g/cm}^3$. $(NaCl = 58.5 \, \text{g/mol})$

The density of $KBr$ crystal is $2.75 \, g/cm^3$ and the edge length of the unit cell is $654 \, pm$. Calculate the number of formula units per unit cell and identify the type of unit cell. $(K = 39 \, u, Br = 80 \, u)$.

At $T \ K$, copper (atomic mass $= 63.5 \ u$) has $fcc$ structure with an edge length of $x \ \mathring{A}$. The density of copper (in $g \ cm^{-3}$) at that temperature is approximately $(N_A = 6.0 \times 10^{23} \ mol^{-1})$

The density of $Na$ is $0.613 \ g \ cm^{-3}$. If the edge length of the unit cell of $Na$ is $5 \ \mathring{A}$,the effective number of atoms of $Na$ per unit cell is (Atomic weight of $Na = 23 \ u$)

The second order Bragg's diffraction of $X$-rays with $\lambda = 1 \ \mathring{A}$ from a set of parallel planes in a metal occurs at an angle of $60^\circ$. The distance between the scattering planes in the crystal is ................ $\mathring{A}$.

An element has a $bcc$ structure. If its edge length is $250 \, pm$ and its density is $8 \, g/cm^3$,calculate its molar mass and the radius of the atom.