Final answer:
The electromagnetic force is responsible for attracting the opposite poles of two bar magnets towards each other.
Step-by-step explanation:
The force responsible for attracting the opposite poles of two bar magnets towards each other is the electromagnetic force.
The electromagnetic force is the force that acts between electrically charged particles and is responsible for the interaction between magnets. In the case of bar magnets, the opposite poles have opposite charges (north pole has a positive charge, south pole has a negative charge), so they attract each other due to the electromagnetic force.
The correct answer to the question is b) Electromagnetic force.