The half-life of bromine-74 is 25 min. How much of a 4.0mg sample is still active after 75 min?
What is the remaining mass of a 4.0 mg sample of bromine-74 after 75 minutes, given that its half-life is 25 minutes?
a) 0.50 mg
b) 1.0 mg
c) 2.0 mg
d) 0.25 mg
e) 4.0 mg
3 Answers
75/25 = 3 and that means 3 half-lives have passed. So activitiy will be (1/2)^3 = 1/8th of the original. Since original quantity is given as 4 mg, 1/8th will be 0.5 mg.
Answer a is right.
Half life is that time by when half the original radioactive substance decays.
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