Which of the following processes occurs during the reaction of $Cu$ with $AgNO_3$ solution?

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 a solution of $AgNO_3$,if $Cu$ is added,the solution becomes blue due to:

In the reaction $H_2S + NO_2 \to H_2O + NO + S$,$H_2S$ is

Which of the following represents the most oxidized form of hydrocarbon?

In which process does the nitrogen undergo oxidation?