consists 0.012% of the potassium in nature. The human body comprises 0.35% potassium by weight. Calc — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Total K mass = $0.0035 \times 75000 = 262.5 \text{ g}$. Mass of $\text{K}^{40} = 0.00012 \times 262.5 = 0.0315 \text{ g}$. Number of atoms $N = \frac{0.0315}{40} \times 6.022 \times 10^{23} \approx 4.74 \times 10^{20}$. $\lambda = \frac{0.693}{1.3 \times 10^9 \times 3.15 \times 10^7} \approx 1.69 \times 10^{-17} \text{ s}^{-1}$. Activity = $\lambda N \approx 8017 \text{ dps}$. Therefore, correct answer is A.