Thermal reduction of phosphate rock:\nIn the electric furnace route to elemental phosphorus, the fusion/reaction zone is maintained at approximately ________ °C.

Introduction / Context:
Elemental phosphorus can be produced by the electric furnace process, which reduces phosphate rock (apatite) in the presence of carbon and silica at very high temperatures. The correct temperature range of the fusion/reaction zone is an essential fact for process design and safety, influencing energy demand, refractory selection, and product vaporization behavior.

Given Data / Assumptions:

• Feed: phosphate rock (often fluorapatite), silica, and coke/carbon.
• Objective: produce elemental phosphorus vapor for subsequent condensation.
• Question asks for the typical fusion zone temperature range.

Concept / Approach:
In the electric furnace, phosphate is reduced at temperatures well above 1200 °C. The reaction zone is commonly controlled around 1400–1500 °C to achieve sufficient kinetics and phase behavior while managing refractory integrity. Lower ranges (e.g., 250–1050 °C) are insufficient for the main reduction and volatilization of P4, whereas too high temperatures impose material and energy penalties without corresponding benefits.

Step-by-Step Solution:
Identify the thermal reduction chemistry requiring very high temperature.Consult known operating envelopes: industrial practice clusters near 1400–1450 °C in the fusion zone.Select the matching range from the options.

Verification / Alternative check:
Process descriptions and furnace design references consistently report reaction zones around 1400–1500 °C for efficient phosphorus liberation and off-gas handling.

Why Other Options Are Wrong:
250–300 and 500–750 °C are far below the necessary threshold; 950–1050 °C may permit some reactions but not efficient P4 volatilization; 1700–1800 °C is higher than typical and stresses refractories.

Common Pitfalls:
Confusing calcination or preheating temperatures with the primary reduction zone temperature.

Final Answer:
1400-1450