To protect the instrument from magnetic field, it is completely surrounded by

Step-by-step solution

Magnetic shielding requires surrounding the instrument with a high permeability material that diverts external field lines. Soft ferromagnetic materials exhibit this property due to their exceptionally high magnetic permeability. When placed in an external magnetic field, soft ferromagnetic substances channel field lines through themselves, reducing the field strength within the enclosed region to negligible levels. Diamagnetic and paramagnetic materials possess much lower permeabilities and are ineffective for thi