When placed in a magnetic field, which of the materials listed will maintain the highest permeability?

Correct Answer: Option D — Soft iron

Soft iron exhibits exceptionally high magnetic permeability compared to non-magnetic materials like glass, bakelite, or aluminum. Under IEEE 45 and Title 46 CFR Subchapter J principles, it readily concentrates magnetic flux lines, making it ideal for electromagnetic cores and effective shielding applications.