Question

A sample of ₅₃I¹³¹ as iodide ion was adminstered to a patient in a carrier consisting of 0.10 mg of stable iodide ion. After 4 days 67.7% of initial radioactivity was detected in the thyroid gland of the patient. What mass of stable iodide ion had migrated to thyroid gland. t_1/2 for iodide ion = 8 day.

Answer 1

Thus iodide ion left is 0.707 part of initially injected sample, however (he rate decreases only 67.7% or 0.677 in 4 days, thus 

If 0.707 is left then iodide ion migrated to thyroid = 1

Thus 0.677 is left then iodide ion migrated to thyroid = 1 x 0.677/ 0.707 = 0.958

or 95.8% of the iodide ion is migrated to gland.