what is the net force acting on an object 

The net force is the combined force of all individual forces acting on an object. Newton's First Law can be seen to be the special case in the Second Law when F, the net force, is zero. When that happens, the acceleration a must also be zero.

talk back to him about the sport and show him your expertise or leave the room

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.