why number of octahedral voids is n and tetrahedral voids is 2nplease explain and post if animations also available .

Dear student
Octahedral voids lie at edge centre and body centre.So their contribution per atom will be:-
O.V. = 12*1/4 (edge centre) + 1*1 (body centre)
= 3 +1
= 4
Tetrahedral voids are two at each body diagnol.Since we have four body diagnols therefore total no of voids are 8
Since these voids are lying inside the lattice therefore their contribution will be 1.