How many unit cells are present in a cube-shaped ideal crystal of $NaCl$ of mass $1.00 \ g$? [Atomic masses: $Na = 23, Cl = 35.5$]

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 $= 197 \ g \ mol^{-1} ; N_A = 6 \times 10^{23} \ mol^{-1} )$

$A$ metallic element crystallises in a simple cubic lattice. If the edge length of the unit cell is $3 \mathring{A}$ and the density is $8 \ g/cm^{3}$,what is the number of unit cells in $100 \ g$ of the metal? (Molar mass of metal $= 108 \ g/mol$)

For a simple cubic system,find the ratio of the interplanar distances between the $(100)$,$(110)$,and $(111)$ planes.

An element (molar mass $180 \ g \ mol^{-1}$) has a $BCC$ crystal structure with a density of $18 \ g \ cm^{-3}$. What is the edge length of the unit cell?

$A$ metal crystallizes in two phases,one as $fcc$ and another as $bcc$ with unit cell edge lengths of $3.5 \mathring{A}$ and $3.0 \mathring{A}$,respectively. The ratio of density of $fcc$ and $bcc$ phases approximately is