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 and why?

Seema has to apply greater force than Iqbal because her box is heavier and heavier object will have greater frictional force with the surface of contact. This happens because friction is caused by the interlocking of irregularities in the two surfaces. The force of friction will increase if the two surfaces are pressed harder. Hence, more force is required to push the heavier box.