JEE Main levelSingle correct optionDifficulty 2 of 3mt014
Assertion (A): Sulphide ores are converted into oxides by roasting before they are reduced by carbon.
Reason (R): Reduction of a metal sulphide by carbon to give CSX2 is thermodynamically unfavourable because CSX2 has a positive standard Gibbs energy of formation.
ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
DA is false but R is true
Answer: A
Carbon cannot be used directly on sulphides because forming CSX2 has a positive ΔfG∘ and the coupled reaction stays positive. Roasting converts the sulphide into the oxide, which carbon can reduce, so R explains A.