Which of the following metal is found in gun metal, monel metal and constantan alloys? (a) \(\mathrm{Cu}\) (b) \(\mathrm{Fe}\) (c) \(\mathrm{Hg}\) (d) \(\mathrm{Zn}\)

Gun metal, also known as red brass in the United States, is a type of bronze – an alloy primarily composed of copper (Cu), with tin (Sn) and zinc (Zn) as the secondary components. Its standard composition roughly comprises 88% copper, 10% tin, and 2% zinc, creating a material known for its resistance to corrosion and ability to handle high pressures.

Due to its strength and durability, gun metal is often used in applications where resistance against steam and saltwater is necessary, such as in marine engineering, for valves and gears, and, historically, for making cannons, which is where the name originates. Despite its name, it is not used to make guns today. In educational settings, learning about gun metal's composition helps students understand the properties that an alloy gains from its constituent metals, such as the malleability and thermal conductivity provided by copper, fortified by the hardness of tin.

Monel metal stands out as a remarkable alloy, primarily because it contains a large proportion of nickel (Ni), with copper (Cu) being the secondary significant component. The typical proportions in Monel alloys are approximately 67% nickel and 28% copper, along with traces of iron (Fe) and other elements.

The exceptional quality of Monel metal includes its resistance to corrosion and its strength, which make it an excellent choice for more demanding environments, such as highly corrosive conditions and in the presence of alkaline and acidic substances. This makes Monel suitable for chemical processing equipment, marine applications like ship hulls, and in musical instruments for its acoustical properties. Understanding Monel metal's composition enables students to grasp the concept of creating specific characteristics in an alloy, tailored for unique applications, by altering element ratios.

Constantan is an alloy with a nearly balanced combination of two primary metals, consisting of approximately 55% copper (Cu) and 45% nickel (Ni). This particular mixture bestows the alloy with its unique characteristic of having a low and stable electrical resistivity over a wide range of temperatures.

Due to this property, it's widely used in thermocouples and resistance wire. In educational contexts, discussing constantan alloy helps illustrate the concept of resistance and its temperature dependency, or lack thereof, in certain materials. It serves as an excellent example of how combining different elements can produce an alloy with a distinct and desirable property that neither pure component exhibits, highlighting the importance of alloy composition in practical applications.