Question

How many grams of lead will remain after $6$ hours, if a researcher begins with $2$ grams of lead$-199$. Given that half-life of Lead$-199$ is $1.5$ hours.

• A. $0.125$ grams
• B. $0.25$ grams
• C. $0.375$ grams
• D. $0.5$ grams
• E. $0.625$ grams

Answer 1

The correct option is A $0.125$ grams

From , law of radio of activity, $N=N_0{e}^{-\lambda t}$ where decay constant, $\lambda =\frac{0.693}{t_{1/2}}=0.693/1.5=0.462h{r}^{-1}$

So, $N=2e^{-0.462\times 6}=0.125$ grams