Final answer:
Fusible metal plugs melt at temperatures higher than 100°C, and while the options given do not specify the exact standard temperatures, the option closest to standard ranges is D) 110-120°C. Typical fusible alloys used in safety devices have melting points that include this range or are higher.
Step-by-step explanation:
Fusible metal plugs are designed to melt at specific temperatures for safety reasons, such as in boilers or engines to prevent pressure buildup. These plugs generally have a melting point range that is quite a bit higher than room temperature. While the options provided do not give a precise standard for fusible plug alloys, typical fusible alloys used in plugs melt at temperatures well above 100°C. Therefore, for standard safety devices, none of the options A) 50-60°C, B) 70-80°C, C) 90-100°C would be adequate as they are too low for most applications. Option D) 110-120°C is the closest to the typical melting range for fusible plugs, which often falls within a range that includes these temperatures but can also be significantly higher, depending on the material and specific use case. Understanding heat transfer and melting points is important when dealing with the melting and casting of metals, like making lead slugs for bullets.