In the alumino-thermite process,$Al$ acts as which of the following substances?

The reactions which occur in a blast furnace at $500-800 \ K$ during the extraction of iron from haematite are:
$(i)$ $3 Fe_2O_3 + CO \rightarrow 2 Fe_3O_4 + CO_2$
$(ii)$ $Fe_2O_3 + 3 C \rightarrow 2 Fe + 3 CO$
$(iii)$ $Fe_3O_4 + 4 CO \rightarrow 3 Fe + 4 CO_2$
$(iv)$ $Fe_2O_3 + CO \rightarrow 2 FeO + CO_2$

In the electrolysis of alumina $(Al_2O_3)$,cryolite $(Na_3AlF_6)$ is added to:

$Ag_2S + NaCN \to (A)$,$(A) + Zn \to (B)$
$(B)$ is a metal. Hence,$(A)$ and $(B)$ are:

Limestone is used as a flux in the extraction of

The flux used to remove the $FeO$ impurity present in the mixture obtained from the roasting of copper pyrites,and its nature,is .....