Which of the following factors is of no significance for roasting sulphide ores to the oxides and not subjecting the sulphide ores to carbon reduction directly?

The primary reason for roasting sulphides to oxides before reduction is that the reduction of metal sulphides with carbon is thermodynamically unfavorable because ${\text{CS}}_2$ is not very stable compared to metal sulphides. In contrast, the reduction of metal oxides with carbon is favorable because ${\text{CO}}_2$ and $\text{CO}$ are very stable. Thus, option A refers to the fact that makes direct reduction difficult.