The surface of all the three bodies is rough and there is a frictional force present whenever any of them slides against the other.
The coefficient of friction between the object weighing 3 kg and the object weighing 2 kg placed below it is `mu` = 0.5. The normal force acting between the two objects is 3*9.8 = 29.4 N. When a horizontal force F is applied to the object weighing 3 kg, the force of friction between the two is 29.4*0.5 = 14.7 N.
Similarly, The normal force between the object with mass 2 kg and the object with mass 1 kg is 5*9.8 = 49 N and the force of friction between the two is 49*0.3 = 14.7 N. The normal force between the object with mass 1 kg and the ground is 6*9.8 = 58.8 N and the frictional force between the two is 58.8*0.1 = 5.8 N.
When the force F applied to the object with mass 3 kg is increased, the slipping starts first between the objects where the force of friction between the two is the least. This is case between the object with mass 1 kg and the ground.
The correct answer is option C.