ANS:A - of the better CaO/SiO₂ balance for slag formation.

Low-grade phosphate rock can be used in an electric furnace because it is cheap. Explanation:

1. Cost-Effectiveness: Low-grade phosphate rock typically contains lower concentrations of phosphorus and may have impurities compared to higher-grade phosphate rock. As a result, it is less expensive to acquire.
2. Availability: Low-grade phosphate rock is often more abundant and readily available compared to higher-grade varieties. This makes it a cost-effective option for use in industrial processes such as phosphate rock beneficiation and phosphoric acid production.
3. Industrial Applications: In industrial processes such as electric furnace reduction of phosphate rock to produce elemental phosphorus or the production of phosphoric acid, low-grade phosphate rock can still be utilized effectively, especially when cost considerations are paramount.
4. Slag Formation: While the CaO/SiO2 balance for slag formation is important in some industrial processes, such as steelmaking, it may not be the primary factor influencing the choice to use low-grade phosphate rock in an electric furnace.
5. Product Cost: By using low-grade phosphate rock, manufacturers can produce phosphorus-based products at a lower cost. This can be advantageous for industries where cost competitiveness is crucial.