A radioactive isotope has a half-life of . If an initial sample contains of this isotope, what mass — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

The number of half-lives ($n$) is $\text{Total Time} / \text{Half-life} = 20 / 5 = 4$. The remaining amount $N_t = N_0(1/2)^n = 256 \times (1/2)^4 = 256 / 16 = 16\text{ g}$.