Calculate the packing efficiency in a simple cubic lattice. 

Explanation

In a simple cubic unit cell, atoms are located only at corners of the cube. The particles touch one another along edge.
Then a is related to `a=2r`.
`"Volume of cubic unit cell is "a^(3)=(2r)^(3)=8r^(3)`
`"Volume occupied by each sphere "4//3pir^(3)`
`"Packing efficiency"=("Volume occupied by each atom")/("Volume of cubic unit cell")xx100=((4)/(3)pir^(3))/(8r^(3))xx100=52.36%`