two half-lives
Express your answer to three significant figures and include the appropriate units.
Two half-lives is approximately equal to 2.000 times the half-life of the radioactive substance being considered. Therefore, the appropriate units would depend on the specific substance being referred to. For example, if the half-life of a certain radioisotope is 5 days, then two half-lives would be equal to 2.000 times 5 days, or 10.0 days.
To calculate the time it takes for two half-lives, you need to know the half-life of the substance in question.
Let's assume the half-life of the substance is 5 hours.
To find the time it takes for two half-lives, you will multiply the half-life by 2 (since you want two half-lives).
2 x 5 hours = 10 hours
So, the time it takes for two half-lives is 10 hours.