A carpenter has a mix of both iron nails and plastic nails in a jar. For a job, he needs only the iron nails. What physical properties could help him separate the nails?

Magnetism

Explanation:

The carpenter can separate the iron nails from the plastic nails using a magnet. The iron nails have magnetic properties therefore they would be attracted to the magnet living only the plastic nails. This process is known as magnetic separation because it is based on the physical properties of the mixed components separating a mixture of components containing magnetic and non magnetic materials.

unable to answer the rest since your question is incomplete

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia