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A human body required 0.01M activity of radioactive substance after 24 hours. Half-life of radioactive substance is 6 hours. Then injection of maximum activity of radioactive substance that can be injected will be:

1. 0.08M
2. 0.04M
3. 0.32M
4. 0.16M

Correct answer: 0.32M

Solution

The activity of a radioactive substance decreases according to the formula A = A₀(1/2)^(t/t₁/₂). Given t = 24 hours and t₁/₂ = 6 hours, the activity reduces by a factor of (1/2)^(24/6) = (1/2)^4 = 1/16. To achieve 0.01M activity after 24 hours, the initial activity A₀ must be 0.01M × 16 = 0.16M.

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