Answer: 16%
Explanation:
The formula to calculate the percent error is given by :-

Given : A pharmacist measured 189 mL using a graduated cylinder.
i.e. The approximate volume =189 mL
Also, volume was again measured using a calibrated standard device, from which it was determined that the volume of the liquid was actually 225.0 mL.
i.e. the Exact volume= 225.0 mL
Now, the percent error in this measurement :-

Hence, the percent error in this measurement = 16%