Metallurgical Processes

A riser, also known as a feeder, is a reservoir built into a metal casting mold to prevent cavities due to shrinkage. Most metals are less dense as a liquid than as a solid so castings shrink upon cooling, which can leave a void at the last point to solidify.

This process is generally used for the concentration of sulphide ores. In this method the ore is taken in an iron tank along with a mixture of water and pine oil. The mixture is vigorously agitated by blowing compressed air. The oil forms a froth with air. The metallic ore particles get stick to the forth and rise to the surface as scum.The impurities are wetted by water and will settle down at the bottom .The froth containing the metallic ore particles is skimmed off and dried.

Cladding is the bonding together of dissimilar metals. It is distinct from welding or gluing as a method to fasten the metals together. Cladding is often achieved by extruding two metals through a die as well as pressing or rolling sheets together under high pressure.

This process is employed for purification of volatile metals like mercury, zinc and cadmium. The impure metal is heated in a retort and its vapours are separately condensed in a receiver. While the pure metal distills over, the non-volatile impurities are left behind in the retort.

Yes, it is a fast change. The changes which take less  time are called fast changes.

Galvanizing is the process of applying a protective zinc coating to iron or steel to prevent rusting. The zinc layer acts as a sacrificial anode, corroding preferentially to protect the underlying metal.

Stainless steel is primarily an alloy of iron, chromium (10-30%), and nickel. Chromium provides corrosion resistance by forming a passive oxide layer, while nickel enhances strength and corrosion resistance. Carbon is present in small amounts but not a primary alloying element.

Galvanised iron is coated with zinc through a process called galvanisation. The zinc layer protects the underlying iron from rusting by acting as a sacrificial anode. Tin is used for tin plates, lead is toxic and not used for galvanising, and chromium is used for chrome plating.

Rusting of iron is a chemical change because iron reacts with oxygen and water to form iron oxide (rust), which has different chemical properties than the original iron. The other options (tempering, melting, bending) are physical changes that don't alter chemical composition.

Galvanization is the process of applying a protective zinc coating to iron or steel. Zinc corrodes preferentially to iron (sacrificial protection), preventing rust. The claimed answer is correct.

This option is correct because calcination is the process of heating the ores strongly in the absence of air and roasting is the process of heating the ores strongly in the presence of excess air.

Barium chromate is a fine light yellow powder with the formula BaCrO_4. It is an oxidizing agent, and produces a green flame when heated, the result of barium ions. It is used as a corrosion inhibitor to prevent electrochemical corrosion at the joints of dissimilar metals.

Barium carbonate (BaCO₃), also known as witherite, is a chemical compound used in rat poison, bricks, ceramic glazes and cement. Witherite crystallises in the orthorhombic system. It is widely used in the ceramics industry as an ingredient in glazes. It acts as a flux, a matting and crystallising agent and combines with certain colouring oxides to produce unique colours not easily attainable by other means.

This option is correct.

This option is correct.