An aliquot of 3.0 mL was taken out

An aliquot of 3.0 mL was taken out from the reaction mixture
at regular time intervals and the absorbance was measured
spectrophotometrically at kmax = 560 nm. It was observed
that the absorbance of the solution decreases with increasing
time intervals, which indicates that the concentration of RB
decreases with increasing time of exposure. A plot of
2+ log A versus time was linear and follows pseudo-firstorder
kinetics. The rate constant was measured using the following
expression: