A radioactive element has atomic mass 90 amu and a half-life of 28 years. The number of disintegrati — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Decay constant $\lambda = \frac{0.693}{28 \times 365 \times 24 \times 3600} \text{ s}^{-1} \approx 7.85 \times 10^{-10} \text{ s}^{-1}$. Number of atoms in 1 gram $N = \frac{1}{90} \times 6.022 \times 10^{23} \approx 6.69 \times 10^{21}$. Activity $A = \lambda N = (7.85 \times 10^{-10}) \times (6.69 \times 10^{21}) \approx 5.25 \times 10^{12} \text{ dps}$. Therefore, correct answer is D.