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

The correct answer is (a) 30% and 26%. In a Cubic Close Packed (CCP) structure, the atoms are arranged in hexagonal layers, and the ratio of atoms to the total space is 3:7. This means that each layer will contain 3 parts atoms, and the remaining 7 parts will remain empty. This gives a free space of 30%. In Body Centred Cubic (BCC) structure, the atoms are arranged over the 8 corners of the cube plus the center. This means that the ratio of atoms to the total space is 2:8. This means that each layer will contain 2 parts atoms, and the remaining 8 parts will remain empty. This gives a free space of 26%.