The ore in which sulphide is absent :

$(I)$ Cuprite      $(II)$ Argentite   $(III)$ Pyrites    $ (IV)$ Siderite

Which of the following factors is of no significance for roasting sulphide ores to the oxides and not subjecting the oxides and not subjecting the sulphide ores to carbon reduction directly ?

When $ZnS$ and $PbS$ minerals are present together, then $NaCN$ is added to separate them in the froth floatation process as a depressant, because

Carnallite does not contain

Match List $-I$ with List $- II$

Choose the most appropriate answer from the options given below.