Which materials can be joined using soldering?

Soldering is a process commonly used to join various metals by melting a filler metal, known as solder, which has a lower melting point than that of the workpieces. This method is particularly effective for creating strong, conductive connections, which is why it is widely used in electrical work, plumbing, and other applications involving metal connections.

The correct choice highlights that soldering can be applied to a range of metals, including but not limited to copper, brass, and silver. These materials are conducive to soldering because they can effectively bond with the solder, ensuring a reliable joint. This versatility is what makes soldering a preferred technique in many industries where metal joints are necessary.

In contrast, focusing solely on plastics or steel ignores the broader applicability of soldering to a variety of metal types, which is crucial in many applications. Plastics typically require different joining methods, such as adhesives, while steel can sometimes be welded instead of soldered, depending on the specific requirements and material properties. Hence, the option stating that soldering is limited to only copper or steel does not capture the full scope of the process.