Potassium crystallizes in a body-centered cubic lattice.  The approximate number of unit cells in 4 g of potassium is a×1022? Atomic mass of potassium = 39. The value of a is

There will be eight atoms at corners of the cube and one atom at the body center.∴ Number of atoms per unit cell =8×18+1×1=2 Number of atoms in 4g of potassium =439×6.023×1023∴ Number of unit cells in 4g of potassium =439×6.023×10232=3.09×1022