Question

The half-life for a 200 gram sample of radioactive element X is 5 days. How much of element X remains after 15 days have passed?

A. 200 g - no change

B. 25 g

C. 50 g

D. 12.5 g

Answer 1

B.) 25g

Step-by-step explanation:

The easiest way to solve this problem is to realize that the sample has gone through three half-lives (15÷5=3).

Use this information to calculate how much of the original 200g sample is left after the three half-lives:

`((1)/(2))(200g)=100g\\((1)/(2))(100g)=50g\\((1)/(2))(50g)=25g`

So, after three half-lives, the remaining sample has a mass of 25g.