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?

Which one of the following is the correct statement?

Larger number of oxidation states are exhibited by the actinoids than those by the lanthanoids, the main reason being :

In which of the following octahedral complexes of Co (at. no. 27), will the magnitude of $$\Delta _o$$ be the highest?