Answer: The correct answer is "wrap more coils of wire around the nail".
Step-by-step explanation:
Electromagnet: When the current passes through iron core wounded by the coils then it will get magnetized. It is not a permanent magnet.
It will loose its magnetism when the current does not flow in it.
The poles of the electromagnet can be changed. They are not fixed.
In the electromagnet, the strength of the magnetism can be increased or decreased by increasing the number of turns in the coil and by increasing the current.
In the given problem, If you make an electromagnet using a battery circuit and a steel nail, the magnetic strength can be increased by wrapping more coils of wire around the nails.
Therefore, the correct option is (B).