Answer: C) The field would reverse its poles.
Step-by-step explanation:
The given diagram shows an electromagnet. A iron nail is placed between coil through which current is passes as it is connected to the battery.
When the terminals are reversed, the current still flows but in the opposite direction. Magnetic field is still generated but with the reversed poles.
Magnetic field produced:
B = μ n I
The direction of the magnetic field reverses with the direction of the current.