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Time to reduce a first order reactant to 10% (by 90%) from its half-life

The same question, asked 3 times: 11 May 2023 S2*, 20 Apr 2025 S2*, 22 Apr 2025 S1. Every wording below, oldest first.

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  1. Question 1

    11 May 2023 S2

    94
    What is the time needed to reduce the initial concentration of reactant to 10% in a first order reaction if its half life time is 10 minutes?

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  2. Question 2

    20 Apr 2025 S2

    85
    Half-life of a first order reaction is 3 minute. What is the time required to reduce the concentration of reactant by 90%90\% of its initial concentration?

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  3. Question 3

    22 Apr 2025 S1

    99
    Half-life of a first order reaction is 20 minutes. The time taken to reduce the initial concentration of reactant to (1/10)th (1/10)^{\text{th~}} is ____\_\_\_\_ .

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