Calculate the density of a metal having molar mass $197 \ g \ mol^{-1}$ if it forms $fcc$ structure. $\left[a^3 \times N_{A}=40 \ cm^3 \ mol^{-1}\right]$ (in $g \ cm^{-3}$)

When an electron in an excited atom jumps from the $L$ shell to the $K$ shell,$X$-rays are emitted. These $X$-rays undergo first-order diffraction at an angle of $7.75^{\circ}$ by a crystal with an interplanar spacing of $2.64 \ \mathring{A}$. Calculate the energy difference between the $K$ shell and the $L$ shell. $(\sin \ 7.75^{\circ} = 0.1349)$

Calculate the volume of a simple cubic unit cell if the radius of the particle in it is $400 \ pm$.

Derive the expression to calculate the density of a unit cell.

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

Calculate the density of a metal with molar mass $56 \ g \ mol^{-1}$ that crystallises in a $bcc$ structure with an edge length of $288 \ pm$. (in $g \ cm^{-3}$)