ANS:D - silica and coke

Silica and coke are both materials commonly used in various industrial processes, including the production of phosphorus through the electric furnace method.

1. Silica (SiO2): Silica is a chemical compound consisting of silicon and oxygen atoms arranged in a tetrahedral structure. It is one of the most abundant minerals on Earth and is commonly found in sand, quartz, and various types of rocks. In the context of the electric furnace method for phosphorus production, silica is sometimes added to the reaction mixture along with coke. Silica serves multiple purposes in this process:
   • It acts as a flux, helping to lower the melting point of the mixture and facilitate the fusion of the raw materials.
   • It reacts with impurities in the phosphate rock, such as iron oxide and alumina, forming slag. The slag floats on top of the molten phosphorus, allowing for easier separation and purification of the phosphorus.
   • It contributes to the overall composition and properties of the slag, which can affect the efficiency and quality of the phosphorus production process.
2. Coke: Coke is a solid carbonaceous material derived from coal or petroleum. It is produced by heating coal or petroleum in the absence of air to drive off volatile compounds and leave behind carbon-rich residue. Coke is a critical component in the electric furnace method for phosphorus production. When mixed with phosphate rock and heated in the electric furnace, coke serves as the reducing agent in the reaction: Ca3(PO4)2+3SiO2+5C→3CaSiO3+5CO+2PCa3​(PO4​)2​+3SiO2​+5C→3CaSiO3​+5CO+2P In this reaction, coke reacts with silica and phosphate rock to produce liquid phosphorus (2P2P) along with carbon monoxide (5CO5CO) as a byproduct. The role of coke is to provide carbon for the reduction of the phosphate rock, facilitating the extraction of elemental phosphorus.