Concept:A magnetic keeper prevents loss of magnetism by completing the magnetic circuit.
Explanation:When a magnet is not in use, its magnetic poles tend to lose strength due to self-demagnetization.
A keeper is a soft iron piece placed across the poles.
It provides a low reluctance path for the magnetic flux.
This keeps the magnetic field lines confined within the keeper.
Thus, the magnet is protected from internal demagnetizing effects.
It does not cancel Earth's magnetism, protect from electric fields, or increase the magnet's strength.
Answer:The correct option is B: reduce self demagnetization.