Which one of the following metals is found in gunmetal, Monel metal, and constantan alloys?

Cu

The correct answer is option 1. Cu.

The metal found in gun metal, monel metal, and constantan alloys is Cu, which stands for copper.

Gun metal is an alloy primarily composed of copper (Cu), tin (Sn), and zinc (Zn). It is commonly used for making firearms, valves, and fittings.

Monel metal is a group of nickel (Ni)-copper (Cu) alloys, with copper being the main component. Monel alloys exhibit excellent corrosion resistance and are commonly used in marine applications and for making valves, pumps, and propeller shafts.

Constantan is an alloy composed mainly of copper (Cu) and nickel (Ni). It is known for its low electrical resistance and high resistivity. Constantan alloys are used in applications requiring precise electrical resistance, such as resistors, thermocouples, and strain gauges.

Therefore, the metal common to all three alloys is copper (Cu).