In the reactions given below,identify the species undergoing oxidation and reduction:
$(i)$ $H_{2}S_{(g)} + Cl_{2(g)} \rightarrow 2HCl_{(g)} + S_{(s)}$
$(ii)$ $3Fe_{3}O_{4(s)} + 8Al_{(s)} \rightarrow 9Fe_{(s)} + 4Al_{2}O_{3(s)}$
$(iii)$ $2Na_{(s)} + H_{2(g)} \rightarrow 2NaH_{(s)}$

(N/A) $(i)$ $H_{2}S$ is oxidised because a more electronegative element,chlorine,is added to hydrogen (or a more electropositive element,hydrogen,has been removed from $S$). Chlorine is reduced due to the addition of hydrogen to it.
$(ii)$ Aluminium is oxidised because oxygen is added to it. Ferrous ferric oxide $(Fe_{3}O_{4})$ is reduced because oxygen has been removed from it.
$(iii)$ With the careful application of the concept of electronegativity,we may infer that sodium is oxidised and hydrogen is reduced.