engineering chemistry MCQ #4944

The half-life of a radioactive substance is 20 years. The time required for 90% decay is

engineering chemistry MCQ #4944

  1. Question 1

    Q1. The half-life of a radioactive substance is 20 years. The time required for 90% decay is

    • A) 66.4 years
    • B) 33.2 years
    • C) 60 years
    • D) 40 years

    Answer: 66.4 years

    Explanation: Using the formula for first-order reactions, t = (2.303 / k) log([A0]/[A]), and k = 0.693 / t1/2, we can find t for 90% decay.