To determine the correct statement about the changes that take place in the energy of the system when two bar magnets are pulled apart, we need to consider the nature of the magnetic forces and the concept of potential energy in magnetic fields.
When two magnets are brought close together, they exert a magnetic force on each other, which can be attractive or repulsive depending on their orientations. If you pull them apart, you are increasing the distance between them, which typically corresponds to an increase in potential energy in the system, especially if the magnets are initially attracting each other.
Since the potential energy associated with the magnetic field increases when you separate magnets that attract each other, the correct statement is:
Potential energy increases because movement is in the opposite direction of the magnetic field.
This means that the pulling apart of the magnets leads to an increase in the potential energy of the system because you're working against the attractive force of the magnetic field.