Iodine-123, which is used for diagnostic imaging in the thyroid, has a half-life of 13 hours. If 50.0 mg of?

The time elapsed is 26 hours. If a half life is 13 hours, 2 half lives have ped. Every time a half life pes, half of the material has decayed. 12.5mg of I-123 remain. (50/2)/2)=12.5. Hope this helps.