The correct answer is A. Solder: Tin.
In the other three pairs, the first word is a mineral or ore that is a source of the second word, which is a metal. Solder, on the other hand, is an alloy of tin and lead that is used to join metal objects.
- Haematite is an iron ore that is the primary source of iron.
- Bauxite is an aluminum ore that is the primary source of aluminum.
- Malachite is a copper ore that is the primary source of copper.
