Final answer:
The correct combination of gases for flame cutting of ferrous materials is oxygen-acetylene, which provides high temperatures necessary for effective cutting.
Step-by-step explanation:
The combination of gases that may be used for flame cutting of ferrous materials is oxygen-acetylene. This mixture is highly effective due to the very high temperatures obtained when acetylene burns in oxygen, which can exceed 3000°C. The oxy-acetylene torch is a crucial tool in many industries for cutting and welding metals due to the net heat of combustion being 1300 kJ/mol. While other gases like natural gas and butane can be used in certain circumstances, oxygen-acetylene is the standard choice for cutting ferrous materials.