In blast-furnace practice, the flux is chosen to combine chemically with the predominant impurity (gangue) in the ore and form a fusible slag. Match impurity to the appropriate flux choice and identify the correct comprehensive statement.

Introduction / Context:
Successful smelting depends on maintaining an appropriate slag basicity so that gangue combines into a fluid phase separable from hot metal. The flux selection always aims to neutralize the chemical character of the impurity: add basic flux to acidic gangue and vice versa.

Given Data / Assumptions:

• Siliceous impurities (clay, quartz) are acidic.
• Limestone (CaCO3) is a basic flux producing CaO on calcination.
• To counter basic gangue, silica-bearing materials can balance the slag chemistry.

Concept / Approach:

For silica-rich gangue (clay/quartz), limestone supplies CaO to form calcium silicates in slag. If the ore already brings excess basic material (limestone), adding clay or siliceous ore raises acidity to restore target basicity. Argillaceous iron ores bring silica and alumina that help tune slag properties when quartz is the dominant impurity.

Step-by-Step Solution:

Verification / Alternative check:

Slag design charts plot basicity ratio (CaO + MgO)/(SiO2 + Al2O3), confirming why balance is required for fluidity and sulfide capture.

Why Other Options Are Wrong:

None of the above: incorrect because each pairing reflects standard flux–gangue balancing logic.

Common Pitfalls:

Treating limestone as universal without checking gangue chemistry; ignoring alumina content that also influences viscosity and melting point.

Final Answer:

All the above