Which of the following factors is not relevant for roasting sulphide ores to oxides and not subjecting the sulphide ores to carbon reduction directly?

Metal sulphides are more stable than corresponding oxides and that is why it is more difficult to extract metal from sulphide ore. To make the extraction easy and economical, first these sulphides are converted into their corresponding oxides and from these oxides metal is easily extracted by reducing them with carbon.