Metallurgical Processes

The fine duct of aluminium is used in paints and lacquers. For cutting tools and crushing machines chrome steel is used.

For making cables, automobiles and aeroplane part – nickel steel is used. But copper dust is not used as a reducing agent in the manufacture of dyestuffs and paints. So this second is the mismatch.

Correct option is B.

Zinc is used for galvanising iron to protect it from rusting. Using a less reactive metal than iron would allow iron to get in contact with air & moisture somehow which will lead to peeling up of the covering metal. Zinc is used because Zn corrodes faster than Iron protecting the Fe surface from corrosion.

The formation of metal oxide on the surface of metal is called anodizing. For example: aluminium oxide is formed on the surface of aluminium when it is exposed to air which prevents its corrosion.

Aluminium is soft silvery metal, yet the surface gets tarnished due to the formation of film of its oxide $Al _2O _3$.
When aluminium is exposed to moist air a thin film of  oxide layer which is thin, hard and adhering.
$4Al+3O _2 \rightarrow 2Al _2O _3$

The metals, which are low in the reactive series, undergo reduction reaction. Their metal oxides react with carbon to reduce the metal oxide to its metal and form an oxide of carbon.
$2CuO+C \rightarrow 2Cu+CO _2$

Recycling steel scrap is significantly more energy-efficient than extracting and processing virgin iron ore, saving approximately 75 percent of the energy required.

Stainless steel is a metal alloy made up of steel mixed with elements such as chromium, nickel, molybdenum, silicon, aluminium, and carbon. The content of these elements is not uniform throughout the solid solution which is a necessary condition to be a homogenous mixture. Thus stainless steel is a heterogeneous mixture.

Alloys are homologous mixtures of metals and cannot be separated into its constituents by physical methods. It is still considered a mixture because it shows the property of its constituents and can have variable composition.

Electroplating is the process of plating one metal onto another by hydrolysis, most commonly for decorative purposes or to prevent corrosion of a metal. Metal cladding is the bonding together of dissimilar metals. It is different from fusion welding or glueing as a method to fasten the metals together. In metal spraying a wide range of metals is sprayed onto the surface of another metal. All of these methods are used to prevent corrosion.

Rusting of iron is a redox reaction because iron is oxidised from $0$ to $+3$ oxidation state and oxygen is reduced from $0$ to $-2.$

Coating of iron with zinc to prevent corrosion is called galvanization.
Steel is dipped in a bath of molten zinc. The zinc coated iron is called galvanized iron. Zinc $(E^o=-0.763 : V)$ is stringer reducing agent than iron $(E^o=-0.44 : V)$ and is more easily oxidized than iron . Thus during corrosion, Zn is oxidized instead of Fe.

Iron reacts with air to form iron oxide(III) which is known by the name rust or rusting of iron. Rust is an iron oxide or red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Rust consist of hydrated iron oxide.

Rusting of iron takes place only when both air and moisture are present.

An action of air and water gradually eats up the metal. This eating up of metals by the action of air and moisture on their surface is called corrosion.