The correct option is B I−,Se2−,Br−,O2−,F−
When the following five anions are arranged in order of decreasing ionic radius, the correct
sequence is I−,Se2−,Br−,O2−,F−.
Thus, the option (B) is the correct answer.
Note: As we move down the group, the atomic/ionic radii increases as additional shells of electrons are added. In a period, the ionic radii of isoelectronic species decreases with increase in the atomic number. Hence, the ionic radius of O2− is greater than the ionic radius of F−. The same reason is true for the ionic radii of Se2−, and Br−