ANS:C - 50-60% indirect reduction.

In the context of blast furnace operation, the extent of reduction of wustite (FeO) through indirect reduction is an important factor for efficient performance. Wustite (FeO) is an intermediate compound formed during the reduction of iron ore in the blast furnace. The indirect reduction of wustite involves the reaction between carbon monoxide (CO) and iron oxide (FeO) to produce iron (Fe) and carbon dioxide (CO2), according to the following equation: FeO + CO → Fe + CO2 The extent of reduction of wustite refers to the percentage of FeO that is converted into iron (Fe) through this indirect reduction process. Achieving a reduction of wustite in the range of 50-60% is considered optimal for efficient blast furnace performance. Explanation:

1. Optimal utilization of reducing agents: Carbon monoxide (CO) generated from the combustion of coke in the blast furnace serves as the primary reducing agent for the conversion of iron oxide to iron. By ensuring that around 50-60% of wustite is reduced, the available CO is effectively utilized for iron production without excessive wastage.
2. Balanced reactions: Maintaining a moderate extent of reduction helps to balance the overall chemical reactions occurring in the blast furnace. Excessive reduction may lead to increased carbon consumption, resulting in higher operating costs and undesirable effects such as increased slag formation. Conversely, insufficient reduction can result in incomplete conversion of iron oxide, reducing iron production rates.
3. Energy efficiency: Operating the blast furnace with a reduction of wustite in the range of 50-60% promotes energy efficiency by optimizing the utilization of carbon resources and minimizing heat losses associated with excessive reactions.
4. Quality of iron produced: The extent of reduction can also impact the quality of the iron produced in terms of its purity and mechanical properties. Maintaining optimal reduction conditions helps to ensure the production of high-quality molten iron suitable for further processing.