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The half-life of bromine-74 is 25 min. How much of a 4.0mg sample is still active after 75 min?

a) 0.50mg b)1.0mg c)2.0mg d)0.25mg e)4.0mg
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3 Answers

M
Major Spinka DVM

Feb 20, 2025

a) 0.5mg 3 x 25 mins means half three times.4mg > 2mg > 1mg > 0.5mg :o)... Show More
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M
Major Spinka DVM

Feb 20, 2025

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.... Show More
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M
Major Spinka DVM

Feb 20, 2025

It’s halved every 25 minutes, so …after 25 mins 2mgafter 50 mins 1 mgafter 75 mins 0.5 mgHope this helps... Show More
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