Final answer:
Without knowing the final absorbance value, we cannot calculate the percentage decrease.
Step-by-step explanation:
To calculate the percentage decrease in absorbance, we need to first determine the initial and final absorbance values. The initial absorbance is given as 0.326 at 260 nm. However, there is no information provided about the final absorbance. Without this information, we cannot calculate the percentage decrease. Please provide the final absorbance value to proceed with the calculation.