The half-life of iodine-131 is 8 days. Chan Hee examines two samples of iodine-131. Sample 1 : 10 g Sample 2 : 20 g What can Chan Hee expect to observe about the samples after 16 days?

After 16 days, two half-lives have passed because each half-life is 8 days. After two half-lives, one-fourth of each sample remains as iodine-131, so three-fourths has decayed. That means 7.5 g of the 10 g sample and 15 g of the 20 g sample will have undergone decay. The correct choice is “Three-fourths of each sample will have undergone radioactive decay.”

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