Question

While sulphur dioxide and hydrogen peroxide can act as oxidising as well as reducing agents in their reactions, ozone and nitric acid act only as oxidants. Why? 

Answer 1

In sulphur dioxide (SO₂), the oxidation number (O.N.) of S is +4 and the range of the O.N. that S can have is from +6 to –2. 

Therefore, SO₂ can act as an oxidising as well as a reducing agent. 

In hydrogen peroxide (H₂O₂), the O.N. of O is –1 and the range of the O.N. that O can have is from 0 to –2. O can sometimes also attain the oxidation numbers +1 and +2. 

Hence, H₂O₂ can act as an oxidising as well as a reducing agent. In ozone (O₃), the O.N. of O is zero and the range of the O.N. that O can have is from 0 to –2. Therefore, the O.N. of O can only decrease in this case. Hence, O3 acts only as an oxidant. 

In nitric acid (HNO₃), the O.N. of N is +5 and the range of the O.N. that N can have is from +5 to –3. Therefore, the O.N. of N can only decrease in this case. Hence, HNO₃ acts only as an oxidant.