What is the atomic radius of polonium if it crystallises in a simple cubic structure with edge length of unit cell $$336 \mathrm{~pm}$$ ?

Identify the type of unit cell that has particles at the centre of each face in addition to the particles at eight corners of a cube?

How many atoms of niobium are present in $$2.43 \mathrm{~g}$$ if it forms bcc structure with density $$9 \mathrm{~g} \mathrm{~cm}^{-3}$$ and volume of unit cell $$2.7 \times 10^{-23} \mathrm{~cm}^3$$ ?

How many tetrahedral voids are present in 0.4 mole of a compound that forms hcp structure?