Answer: 10 half-lives.
- A 3 half-lives
- B 7 half-lives
- C 10 half-lives
- D 5 half-lives
Correct answer: C. 10 half-lives
Explanation: 99.9% completion leaves 0.1% (=1/1000) of reactant. Since 2<sup>10</sup> = 1024 is about 1000, this needs about 10 half-lives.
First-order decay curve: concentration halves every t½, and that half-life is constant - a defining test for first-order kinetics.
Concept context
Study the speed of reactions and what affects it: concentration, temperature, and catalysts. Covers rate law, order of reaction, the Arrhenius equation, and reaction mechanisms step by step.