A certain radioactive element has a half-life of one hour.If you start with a 1-g sample of the element at noon,how much of this same element will be left at 3:00 PM?
A)0.5 gram
B)0.25 gram
C)0.125 gram
D)0.0625 gram

Question

Quizplus · Accepted Answer

Since the half-life of the element is one hour, after one hour (at 1:00 PM), half of the original 1-g sample (i.e., 0.5 g) will remain. At 2:00 PM, another half-life will have passed, leaving only 0.25 g (i.e., half of 0.5 g) of the element. Finally, at 3:00 PM (after three half-lives), the remaining amount of the element will be:

0.25 g × (1/2) × (1/2) × (1/2) = 0.125 g

Therefore, the answer is C: 0.125 gram.

A Certain Radioactive Element Has a Half-Life of One Hour