•   An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. It generally consists of wire wound into a coil.

•   When a current is passed through the wire, it creates a magnetic field which is concentrated in the hole in the centre of the coil.

•   Unlike a permanent magnet, the strength of an electromagnet can be changed by changing the amount of electric current that flows through it.

•   Electromagnets will heat up very fast and energy can get lost in the form of heat. So the metal most suitable must have a low heating loss.

•   A good electromagnet is supposed to have low retentivity and low coercivity. So, out of the given four metals, soft iron has the least energy loss per cycle and it gets magnetised and demagnetised easily, and it is thus used in electromagnets.

•   The ability of the magnetic field to remain in the material even after disconnecting from the external source is known as Retentivity.

•   The minimum value of the magnetising intensity necessary to demagnetize the material is known as  Coercivity.

•   Soft Iron is iron that has a low carbon content and is easily magnetized and demagnetized.

•   Soft iron means "annealed iron" which has high values of permeability and lower reluctance.

•   A ferromagnetic material is a substance that can possess magnetization in the absence of an external magnetic field.

•   There are two groups of magnetic materials as soft magnetic materials and hard magnetic materials.

•   Iron is a good example of a ferromagnetic material. Iron also can be found in two types as hard iron and soft iron.

•   This classification is done based on the magnetic properties of iron.

•   The main difference between hard iron and soft iron is that hard iron cannot be demagnetized once it is magnetized whereas soft iron can be demagnetized once it is magnetized.

Properties of Soft iron

•   It gets magnetised faster and has high susceptibility.

•   It loses the acquired magnetism at a faster pace, thus having low retentivity.

•   It is used in electromagnets.

•   Stainless steel is an alloy of iron that is resistant to rusting and corrosion.

•   It contains at least 11% chromium and may contain elements such as carbon, other nonmetals, and metals to obtain other desired properties. Stainless steel's resistance to corrosion results from chromium, which forms a passive film that can protect the material and self-heal in the presence of oxygen.

•   The alloy's properties, such as luster and resistance to corrosion, are useful in many applications. Stainless steel can be rolled into sheets, plates, bars, wire, and tubing.

•   These can be used in cookware, cutlery, surgical instruments, major appliances, vehicles, construction material in large buildings, industrial equipment (e.g., in paper mills, chemical plants, water treatment), and storage tanks and tankers for chemicals and food products.

•   Most stainless steels are first melted in electric-arc or basic oxygen furnaces and subsequently refined in another steelmaking vessel, mainly to lower the carbon content.

•   In the argon-oxygen decarburization process, a mixture of oxygen and argon gas is injected into the liquid steel. By varying the ratio of oxygen and argon, it is possible to remove carbon to controlled levels by oxidizing it to carbon monoxide without also oxidizing and losing expensive chromium.

•   Thus, cheaper raw materials, such as high-carbon ferrochromium, may be used in the initial melting operation.

•   Cobalt is a chemical element with the symbol Co and atomic number 27.

•   As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron.

•   The free element, produced by reductive smelting, is a hard, lustrous, silver metal.

•   Cobalt-based blue pigments (cobalt blue) have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the color was for a long time thought to be due to the known metal bismuth.

•   Miners had long used the name kobold ore (German for goblin ore) for some of the blue-pigment-producing minerals; they were so named, because they were poor in known metals, and gave off poisonous arsenic-containing fumes when smelted.

•   In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold.

•   Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity.

•   A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.

•   Copper is one of the few metals that can occur in nature in a directly usable metallic form (native metals).

•   This led to very early human use in several regions, from circa 8000 BC.

•   Thousands of years later, it was the first metal to be smelted from sulfide ores, circa 5000 BC; the first metal to be cast into a shape in a mold, c. 4000 BC; and the first metal to be purposely alloyed with another metal, tin, to create bronze, c. 3500 BC.

•   Native copper is found at many locations as a primary mineral in basaltic lavas and also as reduced from copper compounds, such as sulfides, arsenides, chlorides, and carbonates. (For mineralogical properties of copper, see the table of native elements.)

•   Copper occurs combined in many minerals, such as chalcocite, chalcopyrite, bornite, cuprite, malachite, and azurite. It is present in the ashes of seaweeds, in many sea corals, in the human liver, and in many mollusks and arthropods.

•   Copper plays the same role of oxygen transport in the hemocyanin of blue-blooded mollusks and crustaceans as iron does in the hemoglobin of red-blooded animals.

•   The copper present in humans as a trace element helps catalyze hemoglobin formation.