Percentage of free space in cubic close packed structure and in body centred packed structure are respectively

$$\text{Percentage of Free Space} = 100\% - \text{Packing Efficiency}$$

1. Cubic Close Packed (CCP) Structure

• Packing Efficiency: A cubic close packed (or face-centered cubic, FCC) structure is highly efficient, with particles occupying 74% of the total volume.
• Free Space:

  $$100\% - 74\% = 26\%$$

2. Body-Centred Packed (BCC) Structure

• Packing Efficiency: A body-centered cubic structure is slightly less densely packed, with particles occupying 68% of the total volume.
• Free Space:
  $$100\% - 68\% = 32\%$$