Packing efficiency of crystals

Assertion:Packing efficiency of body centred cubic structure is 68% Reason:68% is the maximum packing efficiency any crystal can have

What will be approximate packing efficiency of the crystal which forms FCC with half the tetrahedral and octahedral voids occupied without disturbing the lattice?

Calculate the packing efficiency of a metal crystal for a simple cubic lattice.

The packing efficiency of a simple cubic crystal with an interstitcal atom exctly fitting at the boby center is :

The packing efficiency of the 2D square unit cell shown below is