Correct Answer: D
Explanation:
"Soft" (annealed) iron is used in magnetic assemblies, electromagnets and in some electric motors; and it can create a concentrated field that is as much as 50,000 times more intense than an air core.
Iron is desirable to make magnetic cores, as it can withstand high levels of magnetic field without saturating (up to 2.16 teslas at ambient temperature.)
It is also used because, unlike "hard" iron, it does not remain magnetized when the field is removed, which is often important in applications where the magnetic field is required to be repeatedly switched.