Sulphide ores of metal are usually concentrated by froth floatation process. Which one of the following sulphide ores offer an exception and is concentrated by chemical leaching?

The correct option is D Argentite
Leaching process involves the treatment of the ore with a suitable reagent as to make it soluble while impurities remain insoluble. The ore is recovered from the solution by suitable chemical method. Argentite or silver glance, $A{g}_{2}S$ is an ore of silver. Silver is extracted from argentite by the Mac-Aurthur and Forest cyanide process (leaching process).

$A{g}_{2}S+4NaCN\to 2NaAg(CN{)}_2+N{a}_{2}S$

$2NaAg(CN{)}_2+Zn\to N{a}_{2}Zn(CN{)}_4+2Ag$