Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force ?

Force of friction arises because of interlocking of irregularities on the two surfaces in contact. When a heavy object is placed on the floor, the interlocking of irregularities on the surface of box and floor become strong. This is because the two surfaces in contact are pressed harder. Hence, more force is required to overcome the interlocking. Thus to push the heavier box, Seema has to apply a greater force than Iqbal.