In ironmaking and blast-furnace practice, which of the following statements are correct with respect to roasting needs, slag behavior, and casting practice? Choose the most comprehensive correct choice for civil/metallurgical engineering exams.

Introduction / Context:
Blast-furnace ironmaking relies on a sequence of operations and materials behavior: ore preparation, fluxing to form slag, and casting of hot metal. This question checks whether you can connect roasting requirements with slag chemistry and the traditional pig-casting arrangement.

Given Data / Assumptions:

• Ore type may be oxide or sulphide.
• Flux (commonly limestone) forms a fusible slag that carries gangue.
• Traditional casting beds use a central channel (sow) with side moulds (pigs).

Concept / Approach:

Roasting is primarily needed for sulphide ores to drive off sulphur and convert to oxides; oxide ores do not require this preliminary roasting step. In the furnace hearth, lighter slag floats over denser hot metal, enabling separation. Basic blast-furnace slag typically contains a major fraction of CaO from limestone; a representative range allows recalling “around 45% CaO” as a reasonable statement. Casting practice historically sends metal down a main channel (sow) feeding lateral pigs, which inspired the term “pig iron”.

Step-by-Step Solution:

Verification / Alternative check:

Metallurgy handbooks corroborate the role of roasting only for sulphide ores, the buoyant separation of slag, typical CaO percentages in basic slag, and traditional sow–pig casting practice for pig iron.

Why Other Options Are Wrong:

Individually, A–D are all true statements; choosing just one is incomplete. Only the cumulative option captures the complete, correct set.

Common Pitfalls:

Assuming all ores require roasting; confusing slag composition with absolute fixed numbers; forgetting density logic that makes slag float.

Final Answer:

All the above