Huge amounts of radioactive ${^{131}_{53}\textrm{I}}$ were released in the accident at Chernobyl in 1986. Chemically, iodine goes to the human thyroid. (It can be used for diagnosis and treatment of thyroid problems.) In a normal thyroid, ${^{131}_{53}\textrm{I}}$ absorption can cause damage to the thyroid.

1. Write down the reaction for the decay of ${^{131}_{53}\textrm{I}}$.
2. Its half-life is 8.0 d; how long would it take for ingested ${^{131}_{53}\textrm{I}}$ to become 5.0% of the initial value?
3. Absorbing 1 mCi of ${^{131}_{53}\textrm{I}}$ can be harmful; what mass of iodine is this?