Niobium- 91 has a half-life of 680 years. After 2 comma 040 years, how much niobium- 91 will remain from a 300 point 0 - g sample?

The sample goes through 2,040 ÷ 680 = 3 half-lives. Each half-life cuts the amount in half, so 300.0 g becomes 150.0 g, then 75.0 g, then 37.5 g. Therefore, 37.5 g remains, which is choice B.

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