[Olympiad] A first-order reaction has a half-life of 20 minutes. How long (in minutes) will it take for the concentration of the reactant to fall to 12.5% of its initial value?
- 40 min
- 60 min
- 80 min
- 100 min
📝 Detailed explanation
12.5% remaining means the concentration has halved 3 times (100% -> 50% -> 25% -> 12.5%).Total time = 3 * half-life = 3 * 20 = 60 minutes.