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 Gibbs free energy for the reduction of metal sulfides by the carbon is positive, so the process is not spontaneous. The Gibbs free energy is negative for the reduction of metal oxide by carbon, so the process is spontaneous. The stability of metal sulfides is more than metal oxides and the 2 CO is more stable than 2 CS . Therefore, the (c) option has no significance.