The most suitable material for making the core of an electromagnet is:(a) soft iron    (b) brass   (c) aluminium    (d) steel

The most suitable material for making the core of an electromagnet is soft iron because it has high magnetic permeability and less retentivity, which means it can easily gain magnetic properties when current is passed around it and loses the magnetic properties as the current is switched off.

If it does not lose all its magnetism when current is switched off, then it becomes a permanent magnet.

That's why the soft iron is used as a core in a solenoid produces the strongest magnetism.