Which of the following activities will result in the loss of magnetic properties?
Heating
Hammering
Keeping a magnet idle for a long time
The magnetic properties of a magnet are lost by heating it beyond the Curie temperature (At Curie temperature certain magnetic materials undergo a sharp change in their magnetic properties.). Hammering it repeatedly and keeping it idle for a long time will also result in the loss of magnetic properties. Immersing a magnet in water doesn't lead to loss in magnetic properties.