Oxidation is a loss of electrons and the oxidizing agent is a chemical species that undergoes a chemical reaction in which it gains one or more electrons.
The general electronic configuration of halogens is np5, n=2-6. it needs only one more electron to complete the octet and to attain the stable noble gas configuration
They are having electronegativity character also. therefore they have a high tendency to gain an electron and thus act as a strong oxidizing agent.
Fluorine is most powerful oxidizing agent
Oxidizing ability falls as we go down the group.
Eg: 2F2 + 2H2O –> 4HF + O2
Fluorine oxidises water to oxygen and impossible to do simple solution reaction with it
