A uniform cube of side a and mass m rests on a rough horizontal table. A horizontal force F is applied normal to one of the faces at a point that is directly above the centre of the face, at a height 3a/4 above the base. The minimum value of F which the cube begins to tip about the edge is ....(Assume that the cube does not slide).
A. `(Mg)/3`
B. `2/3 mg`
C. `Mg`
D. `(Mg)/(sqrt(2))`