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?
Starting amount Day5 Day10
100 g
a
25 g
b
50 g
c
75 g
d
100 g
After 5 days, half of the sample remains, so there are 50 grams of element X left (option b).
After another 5 days (10 days in total), half of the remaining sample remains, so there are 25 grams of element X left (option a).