The following drug has a selective distribution to certain region after its administration : A, Iodines,?

I think the one it certainly isnt is adrenaline. Hazarding a guess, I would say Iodine is the odd one out and that it has a tendency to be aculated in the thyroid. All of the others can be determined accurately by blood tests (someone correct me please) whereas, an iodine deficiency is characterized by thyroid hormone levels.