A radioactive isotope has a half-life of . If an initial sample contains of this isotope, what mass — Nuclear Chemistry and Radioactivity Chemistry Question
Question
A radioactive isotope has a half-life of $5\text{ hours}$. If an initial sample contains $256\text{ g}$ of this isotope, what mass remains undecayed after exactly $20\text{ hours}$?
Answer: A
💡 Solution & Explanation
The number of half-lives ($n$) is $\text{Total Time} / \text{Half-life} = 20 / 5 = 4$. The remaining amount $N_t = N_0(1/2)^n = 256 \times (1/2)^4 = 256 / 16 = 16\text{ g}$.
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