A meteorite contains 0 point 1 7 g of nickel- 59 , a radioisotope that decays to form cobalt- 59 The meteorite also contains 5 point 2 7 g of cobalt- 59 How many nickel- 59 half-lives have passed since the meteorite formed?

The meteorite’s original nickel-59 amount is the nickel-59 still present plus the cobalt-59 produced: 0.17 g + 5.27 g = 5.44 g. The fraction of nickel-59 remaining is 0.17 ÷ 5.44 = 1/32. Since 1/32 = (1/2)^5, five half-lives have passed, so the answer is choice C, 5.

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