In the following reaction $Cr_2O_7^{2-} + 14H^{+} + 6I^{-} \to 2Cr^{3+} + 7H_2O + 3I_2$,which element is reduced?

In the reaction $8 \ Al + 3 \ Fe_3O_4 \to 4 \ Al_2O_3 + 9 \ Fe$,the number of moles of electrons transferred by $1 \ mol$ of reductant is:

In the reaction,$SO_2 + 2H_2S \longrightarrow 3S + 2H_2O$,the substance that is oxidised is

When $HCl$ reacts with finely powdered iron,it forms ferrous chloride and not ferric chloride. Why?

When $Sn^{2+}$ changes to $Sn^{4+}$ in a reaction:

When ammonia is heated with cupric oxide,the ammonia molecule $.......$