When sulphur reacts with hot and concentrated sulphuric acid, it undergoes a redox reaction where sulphur acts as a reducing agent and sulphuric acid acts as an oxidizing agent. The reaction can be represented as follows:

S + 2H2SO4 → 3SO2 + 2H2O

In this reaction, sulphur atoms (S) are oxidized from a zero oxidation state to a +4 oxidation state in sulphur dioxide (SO2), while the hydrogen atoms (H) in sulphuric acid (H2SO4) are reduced from a +1 oxidation state to a zero oxidation state in water (H2O).

Sulphur dioxide gas is released as a colourless gas with a pungent odour. The hot and concentrated sulphuric acid solution serves as both a reactant and a reaction medium, providing the necessary conditions for the oxidation of sulphur. This reaction is often used in the industrial production of sulphur dioxide, which is subsequently utilized in various applications such as the refining of petroleum, production of paper, and as a bleaching agent in the textile industry.