ANS:B - alloying with cobalt.

The magnetic permeability of iron is increased by alloying with cobalt. Alloying iron with cobalt increases its magnetic permeability, making it more responsive to magnetic fields. This is due to the unique magnetic properties of cobalt, which enhances the overall magnetic behavior of the iron-cobalt alloy. Iron-cobalt alloys, commonly known as permalloys, are widely used in the production of magnetic materials for applications such as transformers, magnetic recording media, and magnetic sensors.