A 64 g sample of a radioisotope has a half-life of 2 hours. What mass of the isotope remains undecayed after 8 hours?
Correct answer C. 4 g
Explanation
Number of half-lives = 8/2 = 4, so the mass remaining = 64 × (1/2)⁴ = 64/16 = 4 g of the original isotope.
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