Answer:
[tex]6[/tex]Explanation:
Here, we want to get the number of half-lives that would have elapsed
Firstly, we need to get the number of 20 minutes in 2 hours
In two hours, since there are 60 minutes in an hour, there would be a total of 120 minutes
Now, the number of 20 minutes in 120 minutes would be:
[tex]\frac{120}{20}\text{ = 6 half-lives}[/tex]