A sensitive magnetic instrument can be shielded very effectively from outside fields by placing it inside a box of
(A) teak wood
(B) plastic material
(C) soft iron of high permeability
(D) a metal of high conductivity

Hint:
In order to solve this question, we should know that a magnetic instrument means any object which produces a magnetic field or to examine the magnetic field in laboratory experiments, and therefore it needs to be used carefully. Here we will discuss how magnetic instruments can be shielded from external magnetic fields.




Complete step by step solution:
A sensitive magnetic instrument is one that can easily get disturbed with the presence of an external magnetic field and due to this the measurements and observation done by sensitive magnetic instruments are wrong and they must be shielded from external magnetic fields. The best way to shield a sensitive magnetic instrument is to place the sensitive magnetic instrument inside a box of soft iron of high permeability because the high permeability of iron allows the external magnetic flux to pass easily through it and the instrument remains shielded. So, to shield the sensitive magnetic instrument better place it inside the box of the soft iron core of high permeability.
Hence, the correct answer is option (C) soft iron of high permeability



Therefore, the correct option is C.




Note:
It should be remembered that the permeability of a medium means how easily a fluid can pass through it so the high permeability of iron core means the fluid of magnetic field lines can easily pass through it.