Oxidation is loss of electron and reduction is the gain of electron. Thereby assigning the oxidation number on central atom in each molecule for each conversion will determine oxidation or reduction process. Considering oxidation number of H=+1,O=−2 we get oxidation state as:
(i) Oxidation number of Cl in HClO3→HClO4
H+5ClO3→+7HClO4Oxidation number of
Cl changes from +5 to +7, by losing two electron is oxidation process.
(ii) Oxidation number of N in NH+4→NH3
−3NH+4→−3NH3
Oxidation number of N does not change. Thus its neither oxidation nor reduction.(iii)Oxidation number of N in NO2→N2O4
+4NO2→+4N2O4
Oxidation number of N does not change. Thus its neither oxidation nor reduction.(iv)Oxidation number of S in HSO−3→SO2−4
H+4SO−3→+6SO4 2−
Oxidation number of S changes from +4 to +6, by losing two electron is oxidation process.
(v) Oxidation number of S in H2O2→H2O
H2−1O2→H2−2O
Oxidation number of O changes from -1 to -2, by gaining one electron is reduction process.
Therefore: (i) Oxidation(ii) None(iii) None(iv) Oxidation(v) Reduction