Addition of iron filings to $CuSO_4$ solution causes the precipitation of $Cu$ due to the:

During which of the following changes will an exchange of $5$ electrons take place?

Reduction involves

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 which of the following reactions does the oxidation of nitrogen occur?

What is an oxidation reaction? Explain it with an example.