As per the diagram, we can see that, face 3 and 4 are adjacent, face 3 and 5 are adjacent, and adjacent 4 and 5 are adjacent, so face 3, 4 and 5 are adjacent face. But as per the diagram 1, face 4 and face 6 are adjacent faces. Hence from the above it is clear that face 5 is the opposite face of face 6.