The density of the unit cell of $Li$ is $0.539 \ g/cm^3$ and the edge length of the unit cell is $3.5 \ \mathring{A}$. How many $Li$ atoms are present in a unit cell of lithium? (Atomic mass of $Li = 6.94 \ g/mol$)

Copper (atomic mass $= 63.5$) crystallises in a $fcc$ lattice and has density $8.93 \, g \, cm^{-3}$. The radius of copper atom is closest to $.... \, pm$.

The distance between two nearest $Ag$ atoms is $2.5 \times 10^{-8} \ cm$. The density of its crystal is .......... $g/cm^3$. $(Ag = 108 \ g/mol)$

Lithium forms a body-centred cubic $(BCC)$ structure. The length of the side of its unit cell is $351 \ pm$. The atomic radius of lithium will be: ............. $pm$

$A$ compound has $fcc$ structure. If the density of the unit cell is $3.4 \text{ g cm}^{-3}$,what is the edge length of the unit cell? (Molar mass $= 98.99 \text{ g mol}^{-1}$)

Gold crystallises in $fcc$ lattice. The edge length of the unit cell is $4 \ \mathring{A}$. The closest distance between gold atoms is '$x$' $\mathring{A}$ and density of gold is '$y$' $g \ cm^{-3}$. What are $x$ and $y$ respectively?
$($ Molar mass of gold $= 197 \ g \ mol^{-1} ; N_A = 6 \times 10^{23} \ mol^{-1} )$