The reductant used in the extraction of magnesium from calcined dolomite via Pidgeon's process is

ANS:C - ferro silicon

Ferro silicon is an alloy composed primarily of iron (Fe) and silicon (Si), with small amounts of other elements such as aluminum and calcium. It is commonly used as a deoxidizer and an alloying agent in the production of steel and cast iron. Here's an explanation of ferro silicon:

1. Composition: Ferro silicon typically contains about 75% to 90% silicon and 2% to 8% iron, with the remainder consisting of trace elements such as aluminum, calcium, and carbon. The exact composition may vary depending on the manufacturer and the intended application.
2. Production: Ferro silicon is produced by smelting a mixture of silica (usually in the form of quartz) and iron ore in an electric arc furnace. The silica is reduced to silicon by carbon in the presence of iron, resulting in the formation of ferro silicon alloy. The alloy is then cooled and broken into smaller pieces for further processing or packaging.
3. Properties: Ferro silicon is a hard, brittle material with a metallic luster. It has a high melting point and is relatively inert at room temperature. The presence of silicon in the alloy imparts desirable properties to the final product, such as increased strength, hardness, and resistance to corrosion.
4. Applications:
   • Deoxidizer: Ferro silicon is commonly used as a deoxidizing agent in steelmaking and cast iron production. It reacts with oxygen and other impurities in molten metal to form slag, which can be easily removed from the surface, resulting in cleaner and higher-quality steel or cast iron.
   • Alloying agent: Ferro silicon is also used as an alloying agent to impart specific properties to steel and cast iron. It can increase the strength, hardness, and wear resistance of the alloy, as well as improve its magnetic properties.
   • Inoculant: In foundry applications, ferro silicon can be used as an inoculant to promote the formation of graphite in cast iron, improving its machinability and reducing the risk of shrinkage defects.
   • Other applications: Ferro silicon finds use in various other industries, including the production of aluminum alloys, welding fluxes, and chemical compounds.