*Question T7D08:
Which of the following types of solder should not be used for radio and electronic applications?*  

*Correct Answer is  A: Acid-core solder*  

### AI Response: (may contain errors)  

The correct answer is **A: Acid-core solder**. 

### Explanation:

1. **Why Acid-core solder is incorrect:**
   - Acid-core solder contains an acidic flux that is designed for plumbing applications. This type of flux can corrode electronic components and circuit boards, leading to poor connections and potential failure of the electronic device. Therefore, it should not be used in radio and electronic applications.

2. **Why the other choices are correct:**
   - **B: Lead-tin solder**: This is a common type of solder used in electronics. It has good electrical conductivity and is easy to work with. The typical composition is 60% tin and 40% lead, which provides a reliable joint.
   - **C: Rosin-core solder**: This type contains rosin flux, which is non-corrosive and safe for electronic applications. It helps to clean the metal surfaces during soldering, ensuring a good electrical connection.
   - **D: Tin-copper solder**: This is a lead-free solder that is also suitable for electronics. It is often used in applications where lead-free solder is required, such as in RoHS-compliant devices.

### Useful Rules of Thumb:
- Always use solder with a flux that is appropriate for the application. For electronics, rosin-core or lead-tin solder is preferred.
- Avoid using any solder that contains corrosive fluxes, such as acid-core solder, to ensure the longevity and reliability of electronic connections.