Explain how energy can be conserved if a substance must gain or lose thermal energy to change state.

float.

archimedes' principle

denser than water sinks in water.

denser than mercury would sink in it

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.