Answer:
Bromine atom would have smallest radius.
Step-by-step explanation:
Comparison between Bromine and Iodine
As we know that on ascending down the group the size of atom increases as a new shell is added on ascending by one step... so Iodine has a greater size than Bromine.
Comparison between Bromine and Bromine ion
As bromine is a halogen atom, so it's ionisation enthalpy is the most in it's period.. so it cannot loose an electron to form a Br+ cation.. so it forms a Br- anion.. by accepting a. electron, so as 1 electron is added to the shell.. the electrons have increased than the no. of protons, so the size would increase as the protons now have to hold more electrons than before, so attraction would decrease. A second reason can also be mentioned as when an electron is added to an atom, it experiences some repulsion from other electrons in same energy shell, so the size would increase. Screening effect of the mid shell electrons also contribute in increasing the size of atom. So Bromine ion would have a greater size than Bromine atom.
By the same analogy the iodine ion would also have grater size than the iodine atom, it also becomes greater in size than the bromine atom..
THUS THE BROMINE ATOM HAS THE LEAST RANKING WHEN ARRANGED IN DECREASING SIZE OF GIVEN SPECIES!!!