A radioactive isotope has a half-life of 4 hours. If you start with 16 g, how much remains after 12 hours?

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Multiple Choice

A radioactive isotope has a half-life of 4 hours. If you start with 16 g, how much remains after 12 hours?

Explanation:
Half-life means the amount remaining is halved every fixed period. After 12 hours, three half-lives have passed since 12 ÷ 4 = 3. So the remaining amount is 16 g × (1/2)^3 = 16 × 1/8 = 2 g. You can see this by halving three times: 16 → 8 → 4 → 2. Therefore, 2 grams remain after 12 hours.

Half-life means the amount remaining is halved every fixed period. After 12 hours, three half-lives have passed since 12 ÷ 4 = 3. So the remaining amount is 16 g × (1/2)^3 = 16 × 1/8 = 2 g. You can see this by halving three times: 16 → 8 → 4 → 2. Therefore, 2 grams remain after 12 hours.

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