Ultimate BOD of a river water sample is 20 mg/L. BOD rate

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Ultimate BOD of a river water sample is 20 mg/L. BOD rate constant (natural log) is 0.15 day^-1. The respective values of BOD (in%) exerted and remaining after 7 days are:

1. 45 and 55
2. 55 and 45
3. 65 and 35
4. 75 and 25

Correct Option: C

Y_u = 20 mg/L
Y₇ = Y_u × e^–kt
= 20 × e^{–0.15 × 7} = 7

% remaining =	7	× 100 = 35%
	20

% exerted = 100 – 35 = 65%