Uranium- 232 has a half-life of 68 point 8 years. After 344 point 0 years, how much uranium- 232 will remain from a 100 point 0 - g sample?

The sample’s age is 344.0 ÷ 68.8 = 5 half-lives. After each half-life, the amount is cut in half, so 100.0 g × (1/2)^5 = 100.0 ÷ 32 = 3.125 g. Rounded to 3 significant figures, about 3.13 g remains, which is choice A.

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