Which of the following correctly represents the process of reduction?

$Zn^{2+}_{(aq)} + 2e^- \to Zn_{(s)}$. This is

When ammonia is heated with cupric oxide,each molecule of ammonia loses how many electrons?

Which of the following phenomena represents oxidation?

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

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: