Carbon-14 has a half-life of 5,730 years. How long will it take for 112.5 g of a 120.0-g sample to decay radioactively? A. 5,730 years. B. 11,460 years. C. 17,190 years. D. 22,920 years

Note that when 60.0 g decays from the 120.0 g sample, one half-life has elapsed. When 30 g decays from the 60.0 g, another half-life has elapsed. When 15 g decays from the 30 g, another half-life has elapsed. So far, 60.0 g + 30.0g + 15.0 g = 90 g have decayed and three half-life have elapsed. When 7.5 g decays from 15.0, you calculate that 90.0 + 7.5g = 112.5 g have decayed in 4 half-life time. So, it will take 4 * 5,730 years = 22,920 years for 112.5 g of a 120.0 g sample to decay radioactively. Answer: option D. 22,920 years