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What percentage of a radioactive substance remains after two half-lives?

User Aroonporn
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2 Answers

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25%

I know this because i have a doctorates in Percents

User Ashish Pancholi
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3 votes

Answer: 25%.

Step-by-step explanation:

  • The decay of a radioactive substance obeys the rules of first order reaction.
  • In first order reaction half life time (t1/2) is constant and does not depend on the initial concentration of the substance (t1/2 = 0.693/k) where k is the rate constant.
  • Half-life time (t1/2) is the time needed for the reaction that the initial concentration of the reactant (substance) reaches its half (reaction be completed by 50 %).
  • radioactive substance (100%) (first half life)50 % (second half life)25 %
  • Hence, the radioactive substance will reach 25 % of its concentration after two half-lives.
User Roger Creasy
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