Sodium metal crystallizes in a body-centred cubic $(bcc)$ lattice with a unit cell edge of $4.29 \ \mathring{A}$. The radius of the sodium atom is approximately ............. $\mathring{A}$.

$A$ compound has $fcc$ structure. If the density of the unit cell is $3.4 \text{ g cm}^{-3}$,what is the edge length of the unit cell? (Molar mass $= 98.99 \text{ g mol}^{-1}$)

The unit cell of an element has an edge length of $5 \mathring{A}$ and a density of $4 \ g \ cm^{-3}$. If its atomic mass is $149 \ g \ mol^{-1}$,identify the crystal structure.

Potassium metal crystallizes in a face-centered cubic $(FCC)$ lattice. If the edge length of the unit cell is $0.574 \ nm$,what is the shortest distance between any two potassium nuclei (in $nm$)?

$A$ metal crystallizes in a $bcc$ unit cell having unit cell volume $2.5 \times 10^{-23} \text{ cm}^3$. Find the number of unit cells in $18 \text{ g}$ of the metal if the density of the metal is $7.2 \text{ g cm}^{-3}$.

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: