# 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? Option 1) $CO_{2}$ is more volatile than  $CS_{2}$ Option 2) Metal sulphides are thermodynamically more stable than $CS_{2}$ Option 3) $CO_{2}$ is thermodynamically more stable than  $CS_{2}$ Option 4) Metal sulphides are less stable than the corresponding oxides

P Prateek Shrivastava

As we learnt in

Roasting -

It is heating of the ore in presence of air below its fusion temperature.

- wherein

2PbS +3O3 $\rightarrow$ 2PbO + 2SO2

The reduction of metal sulphides by carbon reduction has positive  $\Delta G$ whereas, $\Delta G$ is negative for the same process with metal oxides. So, metal sulphides are more stable than oxides.

Option 1)

$CO_{2}$ is more volatile than  $CS_{2}$

This option is incorrect.

Option 2)

Metal sulphides are thermodynamically more stable than $CS_{2}$

This option is incorrect.

Option 3)

$CO_{2}$ is thermodynamically more stable than  $CS_{2}$

This option is incorrect.

Option 4)

Metal sulphides are less stable than the corresponding oxides

This option is correct.

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