Question

difference betweem face centred cell and centred unit cell

Answer 1

Face centred cell means each half of the atoms are present on each face's centre. And where as centered unit cell means the whole atom is present in between the unit cell representing a unit cell

Answer 2

face centered unit cell are those unit cells in which atoms are present at the corner point as well as at each of the faces of the unit cell while in centered unit cell is that in which apart from corners atoms are present at any other pair of faces (but not at every face).