The correct option is B The Gibb's free energy for the formation of most sulphides are greater than that of CS2
The Gibb's free energy for most of the sulphides are greater than that of CS2. In fact, CS2 is an endothermic compound. This means that the reduction of a metal sulphide by carbon to form metal and carbondisulphide is not favorable. Therefore, the ΔrG0 of MxS is not compensated. So, the reduction of MxS is difficult. Hence it is a common practice to roast sulphide ores to their corresponding oxides prior to reduction.