In diamond, carbon atoms occupy $\mathrm{FCC}$ lattice points, as well as alternate tetrahedral voids. If the edge length of the unit cell is $356 \mathrm{pm}$, then the diameter of the carbon atom is:

Copper has a face-centred cubic structure with a unit-cell edge length of $3.61 \mathrm{\AA }$. What is the size of the largest atom (in pm), which could fit into the interstices of the copper lattice without distorting it?

[Hint: Calculate the radius of the smallest circle in the figure.]

The density of a pure substance '$\mathrm{A}$' whose atoms are packed in a cubic-close packed arrangement is $1 \mathrm{g} {\mathrm{cc}}^{-1}$. If $\mathrm{B}$ atoms can occupy tetrahedral void and all the tetrahedral voids are occupied by '$\mathrm{B}$' atoms, what is the density of resulting solid in $\mathrm{g} {\mathrm{cc}}^{-1}?$ $[$Atomic mass $\left(\mathrm{A}\right)=30 \mathrm{g} {\mathrm{mol}}^{-1}$ and atomic mass $\left(\mathrm{B}\right)=50 \mathrm{g} {\mathrm{mol}}^{-1}]$.