Question

question 5 of 10
a sample contains 10 g of a radioactive isotope. how much radioactive isotope will remain in the sample after 2 half - lives?
a. 7.5 g
b. 5.0 g
c. 10.0 g
d. 2.5 g

Explanation:

Step1: Recall half - life formula

The amount of radioactive isotope remaining $N$ after $n$ half - lives, given an initial amount $N_0$ is $N = N_0\times(\frac{1}{2})^n$.

Step2: Identify values of $N_0$ and $n$

Here, $N_0=10$ g (initial amount) and $n = 2$ (number of half - lives).

Step3: Calculate the remaining amount

$N=10\times(\frac{1}{2})^2=10\times\frac{1}{4}=2.5$ g.

Answer:

D. 2.5 g