a) Oxidation: A type of reaction in which oxygen or an electronegative species is added to a substance or there is removal of hydrogen or a positive species from a substance is called oxidation.

For example:

\(CO_2+H_2 \rightarrow CO + H_2)\) (Addition of oxygen to H_2)
\(2Cu+O_2 \rightarrow 2CuO\) (Addition of oxygen to Cu)

b) Reduction: A type of reaction in which hydrogen or an electropositive species is added to a substance or oxygen or an electronegative species is removed, is called reduction.

For example:

\(CO_2+H_2 \rightarrow CO + H_2O\) (Oxygen is removed from \(CO_2\)
\(CuO + H_2 \stackrel{\Delta}{\longrightarrow} Cu + H_2O\) (Oxygen is removed from CuO)