A solid cube is placed on a horizontal on a horizontal surface. The coefficient of friction between them is μ where μ<1/2. A variable horizontal on the cube's upper face, perpendicular to one edge and passing through the the mid-point of edge, as shown in figure. The maximum acceleration with which it can move without toppling is

Drawing FBD of situation from side view

Balancing clockwise and anticlockwise torque at 0
Now; Applying NLM on cube:-