Question

The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?

a
25 g
b
10o g - no change
c
50 g
d
12.5 g

Answer 1

To calculate how much of the radioactive element X remains after 10 days, we can use the concept of half-lives.

The half-life of element X is 5 days. After each half-life, half of the remaining substance is gone.

After 5 days (1 half-life):
- Starting with 100 grams, after 1 half-life (5 days), you have:
\[
100 \text{ g} \div 2 = 50 \text{ g}
\]

After another 5 days (2 half-lives, totaling 10 days):
- From the 50 grams remaining after the first half-life, after another half-life (the second half-life), you have:
\[
50 \text{ g} \div 2 = 25 \text{ g}
\]

So, after 10 days, 25 grams of element X remains.

The answer is **(a) 25 g**.