4. The half-life of cobalt-60 is 5.3 yr. If 2.0 g of cobalt-60 is allowed to decay for a period of 15.9 yr, how many grams of "Co remain? 5. Iodine-135 is a nuclide found in radioactive fallout from nuclear weapon explosions. Its half-life is 6.70 hr. How long, in hours, will it take for 93.75% (15/16) of the "I atoms in a fallout sample to undergo decay? 6. The half-life of cesium-137, a radioisotope used in food irradiation, is 30.2 years. If 4.60 g of cesium-137 is allowed to decay for a period of 90.6 years, how many grams of 137Cs remain? 7. Chromium-151 is a nuclide used in nuclear medicine for the assessment of kidney activity. Its half-life is 27.8 days. How long will it take, in days, for 87.5% of the Cr atoms in a nuclear medicine sample to undergo decay? 8. The half-life of silver-112 is 3.2 hours. How many grams of this nuclide in a 10.0 g sample will have decayed after 28.8 hr.