Final answer:
A furnace is most useful for processing native metals, as it can melt raw ores and metals, which is essential in metal extraction and refinement.
Step-by-step explanation:
If you needed native metals, which tool would be most useful? The correct answer is b. furnace. While a magnet could be useful for picking up ferromagnetic metals like iron, not all native metals are magnetic. A furnace, on the other hand, can be used to process raw ores or native metals by melting them, which is a primary step in extracting and refining metals. A shovel can be used for mining raw materials, but it's not specifically for processing metals. A Geiger counter detects radioactivity and would not be specifically useful in handling native metals unless you're concerned about potential radioactive contamination.
Using magnetism to attract metals is beneficial, but would not necessarily help in processing native metals. Electromagnetic induction can detect buried metal objects and is used in geophysical prospecting, but still requires a furnace or similar tool for metal processing.