SO2 and TeO2 act as respectively are

Oxidation number of sulphur changes from 0 to +4. Due to presence of d-orbitals (vacant) sulphur can extend its covalency and oxidation states till +6, which is stable in sulphur (eg: SF6​).Hence it acts as a reducing agent.Oxidation number of the Tellurium  changes from 0 to +4. Unlike sulphur,  Te  cannot show +6 oxidation state as it is highly unstable due to inert pair effect. Therefore, Te  can only show a decrease in its oxidation state (it can decrease to -2, +2). Hence, it acts as an oxidizing agent.