Which of the following is responsible starch-iodide paper blue when it is brought in contact with O3?

This test paper allows the quick and easy detection of strong oxidizers such as nitrite and free chlorine.Potassium iodide starch paper is also used to control diazotization reaction. Nitrite or free chlorine oxidize potassium iodide to form elemental iodine which reacts with starch to a blue-violet complex. Potassium iodide starch paper may be used by dipping it into the sample or by applying drops of the sample onto the paper.