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For a given water sample, the ratio between BOD5-day, 20°C and the ultimate BOD is 0.68. The value of the reaction rate constant k (on base e)( in day-1, up to two decimal places) is ______ 
    Correct answer is '0.23'. Can you explain this answer?
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    Calculation of reaction rate constant k

    Given data:
    Ratio of BOD5-day, 20C to ultimate BOD = 0.68

    Formula:
    BOD = BODultimate - (BODultimate - BOD5) * e^(-kt)

    Where,
    BODultimate = ultimate BOD
    BOD5 = BOD5-day, 20C
    k = reaction rate constant
    t = time (in days)

    Using the given ratio, we can write:

    0.68 = BOD5 / BODultimate

    Rearranging the equation, we get:

    BODultimate = BOD5 / 0.68

    Substituting the values in the formula for BOD, we get:

    BOD5 / 0.68 = BODultimate - (BODultimate - BOD5) * e^(-kt)

    Simplifying the equation, we get:

    0.68 = 1 - (1 - 0.68) * e^(-kt)

    0.32 = 0.32 * e^(-kt)

    Taking natural logarithm on both sides, we get:

    ln(0.32) = -kt

    Solving for k, we get:

    k = -ln(0.32) / t

    Assuming t = 5 days (as BOD5-day, 20C is given), we get:

    k = -ln(0.32) / 5

    k = 0.23 day^-1 (rounded off to two decimal places)

    Therefore, the value of the reaction rate constant k is 0.23 day^-1.
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    For a given water sample, the ratio between BOD5-day, 20°C and the ultimate BOD is 0.68. The value of the reaction rate constant k (on base e)( in day-1, up to two decimal places) is ______Correct answer is '0.23'. Can you explain this answer?
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