Aluminium crystallizes in an FCC structure. Atomic radius of the metal is 125 pm. What is the length of the side of the unit cell of the metal?

For cubic close packed structure, let a be the edge of the cube and r be the radius of the atom. Given that r = 125 pm.
a = 2√2r
Putting the value of r we get,
2 × 1.414 × 125 pm = 353.5 pm (approximately)