Final answer:
Submerging a magnet in water is NOT a way to demagnetize it. Demagnetization occurs by means such as striking, dropping, or heating the magnet, which disrupt the magnetic domains.
Step-by-step explanation:
The method that is NOT a way to demagnetize a magnet is D) Submerging the magnet in water. Demagnetization methods generally involve disrupting the alignment of magnetic domains within the material. This can be achieved by striking the magnet hard, dropping the magnet, or heating the magnet. These actions can cause enough physical or thermal agitation to disrupt the domain alignment, thereby reducing the magnetic properties. Submerging a magnet in water, however, does not provide the necessary energy or disruption to cause demagnetization.