To obtain a diffraction peak for a crystalline solid with interplane distance equal to the wavelength of incident $X$-ray radiation,the angle of incidence should be $....\,^{\circ}$

The inter-planar spacing between the $(2, 2, 1)$ planes of a cubic lattice of length $450 \, pm$ is $.... \, pm$

Which of the following instruments is used to determine the crystal structure?

An element with density $2.8 \ g \ cm^{-3}$ forms an $fcc$ unit cell having an edge length of $4 \times 10^{-8} \ cm$. Calculate the molar mass of the element.

In a $NaCl$ crystal,the distance between $Na^+$ and $Cl^-$ ions is $2.814 \ \overset{\circ}{A}$ and the density of the crystal is $2.167 \ g/cm^3$. Calculate the value of Avogadro's number $(N_A)$.

In a cubic unit cell of an ionic compound, the eight corners are occupied by anions and cations are at the center of the cube. Calculate the volume of the unit cell if the density of the unit cell is $4 \text{ g cm}^{-3}$. [Molar mass of compound $= 168.6 \text{ g mol}^{-1}$ and $N_A = 6.022 \times 10^{23} \text{ mol}^{-1}$]