Dear student,
Packing efficiency = (vol. of spheres in a unit cell/total vol. of unit cell) ×100
Since CCP has 4 atoms in one unit cell,
PE = (vol. of 4 spheres/volume of cube) ×100
=(4× 4 pi r^3 /3 ×100) ÷ (2r sq.rt.2)^3
=4×4×3.14×r^3 ×100÷ 3×8×r^3 ×2 sq.rt. 2
=3.14×100÷3×1.414
=74 percentage
Cheers!
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