For a crystal,the diffraction angle for the second-order diffraction is $2\theta = 90^{\circ}$. If the distance between two parallel planes is $2.28 \ \mathring{A}$,then the wavelength of the $X$-rays used for Bragg diffraction (in $\mathring{A}$) will be .........

$A$ metal crystallises in a body-centred cubic $(BCC)$ lattice with the metallic radius $\sqrt{3} \ \mathring{A}$. The volume of the unit cell in $m^3$ is:

Iron oxide $FeO$ crystallises in a cubic lattice with a unit cell edge length of $5.0 \ \mathring{A}$. If the density of the $FeO$ in the crystal is $4.0 \ g \ cm^{-3}$,then the number of $FeO$ units present per unit cell is $...........$ (Nearest integer).
Given: Molar mass of $Fe$ and $O$ is $56$ and $16 \ g \ mol^{-1}$ respectively.
$N_{A} = 6.0 \times 10^{23} \ mol^{-1}$

Sodium metal crystallizes as a body-centered cubic $(bcc)$ lattice with the cell edge $4.29 \ \mathring{A}$. What is the radius of a sodium atom?

An atomic substance $A$ of molar mass $12 \ g \ mol^{-1}$ has a cubic crystal structure with an edge length of $300 \ pm$. The number of atoms present in one unit cell of $A$ is $.....$ (Nearest integer). Given the density of $A$ is $3.0 \ g \ cm^{-3}$ and $N_{A} = 6.02 \times 10^{23} \ mol^{-1}$.

$CsBr$ has $b.c.c.$ structure with edge length $4.3 \ \mathring{A}$. The shortest inter-ionic distance between $Cs^{+}$ and $Br^{-}$ is ........... $\mathring{A}$.