In the Goldschmidt thermite process,which substance acts as the reducing agent?

Carbon reduction process is not commercially applicable for which of the following set of oxides to extract the respective metal?
$(I)$ $ZnO$,$(II)$ $Fe_2O_3$,$(III)$ $Al_2O_3$,$(IV)$ $SnO_2$,$(V)$ $MgO$

The slag consists of molten impurities generally in the form of

The term $Smelting$ is used for a process in which ......

The Ellingham diagram is a plot between:

How are the most electropositive metals extracted from their ores?