Answer:
The correct answer option is 3- the magnetic field strength would increase
Explanation:
An electromagnet is a soft metal core which is made into a magnet by passing the electric current through a coil surrounding it.
Unlike a permanent magnet, the strength of an electromagnet can be changed and there are a few factors that effect it.
Since the strength of an electromagnet is directly proportional to not only the number of coils around the solenoid but the current that is passed through it, so replacing a 1.5V battery by a 9V battery will increase its magnetic field strength.