Aseries of experiments, which are repeated over and over, seem to suggest that a scientific theory is incorrect.
what does this most likely mean?

a. the experiments were faulty.
b. the scientist was manipulating the results.
c. the theory must be revised.
d. the results should be modified to agree with the theory.

The theory must be revised.

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.