Which of the following metals is the most reactive?

The following reaction takes place when aluminium powder is heated with $MnO_2$:
$3MnO_2(s) + 4Al(s) \rightarrow 3Mn(l) + 2Al_2O_3(l) + \text{Heat}$
$(a)$ Is aluminium getting reduced?
$(b)$ Is $MnO_2$ getting oxidised?

Which one of the following figures correctly describes the process of electrolytic refining?

Explain the following:
$(a)$ The reactivity of $Al$ decreases if it is dipped in $HNO_3$.
$(b)$ Carbon cannot reduce the oxides of $Na$ or $Mg$.

Which of the following methods is used for the concentration of ore?

$(i)$ Given below are the steps for the extraction of copper from its ore. Write the reactions involved:
$(a)$ Roasting of copper $(I)$ sulphide
$(b)$ Reduction of copper $(I)$ oxide with copper $(I)$ sulphide
$(c)$ Electrolytic refining
$(ii)$ Draw a neat and well-labelled diagram for the electrolytic refining of copper.