(N/A) Redox reactions can be defined as reactions involving the transfer of electrons from one species to another.
Consider the following reactions:
$(1)$ $2 Na_{(s)} + Cl_{2_{(g)}} \rightarrow 2 NaCl_{(s)}$
$(2)$ $4 Na_{(s)} + O_{2_{(g)}} \rightarrow 2 Na_{2}O_{(s)}$
$(3)$ $2 Na_{(s)} + S_{(s)} \rightarrow Na_{2}S_{(s)}$
In these reactions,$Na$ loses electrons to form $Na^{+}$ ions,undergoing oxidation. The non-metals $(Cl_2, O_2, S)$ gain these electrons to form negative ions,undergoing reduction.
For example,in reaction $(1)$:
$2 Na_{(s)} \rightarrow 2 Na^{+} + 2 e^{-}$ (Oxidation)
$Cl_{2_{(g)}} + 2 e^{-} \rightarrow 2 Cl^{-}$ (Reduction)
Overall,$Na$ acts as a reducing agent (electron donor) and the non-metal acts as an oxidizing agent (electron acceptor).