If a metal crystallises in a face-centred cubic $(FCC)$ structure with a metallic radius of $25 \ pm$, the number of unit cells in $1.0 \ cm^3$ of the lattice is:

Niobium crystallises in a body-centred cubic $(bcc)$ structure. If the density is $8.55 \ g \ cm^{-3}$, then the atomic radius of niobium is (atomic mass of niobium $= 93 \ u$) (in $pm$)

If $TlCl$ crystallizes in a $bcc$ structure,then the sum of the radii of the cation and anion will be ........ ($a =$ edge length).

If $a$ stands for the edge length of the cubic systems: simple cubic,body-centred cubic,and face-centred cubic,then the ratio of radii of the spheres in these systems will be respectively:

$A$ metal $M$ crystallizes into two lattices: face-centered cubic $(fcc)$ and body-centered cubic $(bcc)$ with unit cell edge lengths of $2.0 \ \mathring{A}$ and $2.5 \ \mathring{A}$ respectively. The ratio of densities of the $fcc$ lattice to the $bcc$ lattice for the metal $M$ is $...........$ (Nearest integer).

Calculate the number of atoms in $1 \text{ g}$ of a metal that forms a $bcc$ crystal structure. Given that the product of density and unit cell volume is $\rho \times a^3 = 6.6 \times 10^{-22} \text{ g}$.