A solution of sodium iodide containing iodine-131 was given to a patient to test for malfunctioning of the thyroid gland. What fraction of the iodine-131 nuclei would remain undecayed after $7.0 \mathrm{~d}$ ? If a sample contains $2.5 \mu \mathrm{g}$ of ${ }^{131} \mathrm{I}$, how many micrograms remain after $7.0 \mathrm{~d}$ ? The half-life of I-131 is $8.07 \mathrm{~d}$.