A 40.0 gram sample of a radioactive element decays to 5.0 grams in 15 hours. What is the half-life of this element?
A)3 hours
B)2 hours
C)6 hours
D)7)5 hours
E)5 hours

Question

Quizplus · Accepted Answer

In 15 hours, this substance has decayed to 1/8 of its original mass. In other words, the substance has progressed through three half-lives (1/2 x 1/2 x 1/2 = 1/8). Thus, a single-half life for this substance is 5 hours.

A 400 Gram Sample of a Radioactive Element Decays to 5