Question: why teo2 is oxidising agent?
Answer: Its +4 os to +6 os snd can be behave as reducing agent. But in TeO2. ... electrons are reluctant to take part in bond formation due to poor shielding of d- and f-orbitals thus lower oxidation states (+2, -2) becomes more stable( inert pair effect) and hence TeO2 is oxidising reagent.