Which type of solder should not be used for radio and electronic applications?

Acid-core solder is specifically designed for soldering metals such as copper in plumbing applications. It contains an acid flux that helps clean the metal surfaces during the soldering process. However, this type of flux can be highly corrosive and can leave residues that may cause damage to electronic components and circuits over time. In radio and electronic applications, components are often sensitive to corrosion, and any residue left behind by acid-core solder can lead to failures or degrade performance.

In contrast, the other types of solder mentioned, such as lead-tin, rosin-core, and tin-copper, use less harmful fluxes that are suitable for electronic soldering. Rosin-core solder contains a flux derived from natural resin, which is non-corrosive and safe for electronic components. Lead-tin solder is commonly used in electronics due to its reliable electrical conductivity, while tin-copper solder is also a popular lead-free option. Therefore, acid-core solder is not appropriate for radio and electronic applications due to its potential for causing long-term damage.