Final answer:
European merchants were concerned about the supply of gold and silver due to its central role in their economic system, the inflation effects from the influx of these metals causing the Price Revolution, and the necessity to trade with silver in China.
Step-by-step explanation:
European merchants were concerned about the supply of gold and silver because these precious metals were crucial to their economic structures, served as the basis for wealth, and were necessary for international trade. With the massive extraction of gold and silver from the Americas during the age of exploration, Spain became vastly wealthy, which effects rippled through the European economy, leading to a period known as the Price Revolution.
This influx of precious metals began to devalue gold and silver, causing inflation which complicated trade and economic stability for European merchants. Additionally, in the 1500s, the Chinese emperor shifted to silver as their monetary base resulting in a rise in demand for this scarce metal; thus, Europe had to use silver in trade with China, making the supply of silver even more critical to maintain favourable trade positions.