(a) Oxidation: It is defined as a process which involves gain of oxygen. For example,
(i) 2Mg(s) + O2(g) -----> 2MgO(s)
Magnesium Oxygen Magnesium oxide
Here, Mg has gained oxygen to form MgO. Hence, Mg has been oxidised to MgO.
(ii) 2Cu(s) + O2(g) Heat -----> 2CuO(s)
Copper Oxygen Copper oxide
In this reaction, Cu has gained oxygen to form CuO. Thus, Cu is oxidised to copper oxide (CuO).
(b) Reduction: It is defined as the process which involves loss of oxygen. For example,
(i) Cuo + H2 +Heat ------> Cu + H2O
Copper oxide Hydrogen Copper Water
In this reaction, copper oxide is losing oxygen. So, it is being reduced to copper.
