Which of the following types of metals is commonly used as a metallic sheath?

The correct choice regarding the type of metal commonly used as a metallic sheath is lead. Lead is often chosen due to its properties, particularly its ability to provide effective shielding against radiation, which is crucial in various applications, such as in medical and nuclear settings. Its malleability and ductility allow it to be easily formed into sheets and shapes needed for effective sheathing.

While copper is widely known for its excellent electrical conductivity and is used extensively in electrical applications, gold is primarily utilized in high-end electronic connections due to its resistance to corrosion and superior conductive properties. Steel, on the other hand, is used for its strength and durability in structural applications, but it does not offer the same level of radiation shielding as lead. Thus, while all these metals have their unique uses, lead is specifically noted for its effectiveness as a metallic sheath, particularly in contexts where protection from radiation is essential.