question_answer 121)

  Assertion (A) Total number of octahedral voids present in unit cell of cubic close packing including the one that is present at the body centre, is four. Reason (R) Besides the body centre there is one octahedral void present at the centre of each of the six faces of the unit cell and each of which is shared between two adjacent unit cells.  

Answer:

                  (c) Assertion is correct statement but Reason is incorrect statement. Assertion is true as in ccp atom present at face centre and corner of each unit cell which creates octahedral void at each body centre and all twelve edges of a unit cell as shown below Correct reason is that beside the body centre there is one octahedral void at centre of each of 12 edges which is surrounded by six atoms. Out of six atoms four belongs to same unit cell (2 at corner and 2 at face centre) and 2 atoms belongs to adjacent unit cell.