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?

Friction force is directly proportional to mass. Heavier box will put more force on the floor surface as compared to lighter box and therefore will experience more opposite force (friction). Seema will have to apply larger force.

https://www.tiwariacademy.com/ncert-solutions/class-8/science/chapter-12/