Answer:
If the insulating material covered around the can.
Explanation:
If the can is covered with thick layer of insulating material then it can't be attracted by the magnet because there is a gap between magnet and metal. Can is a metal which is attracted by the magnets just like iron and copper etc. If there is no insulating material between magnet and can, then it must be attracted by the magnet so that's why we can say that insulating material is responsible for the no attachment of magnet to the can.
