Correct Response: B. A pH meter must be calibrated with one or more buffer solutions of known pH before use because the meter will not give accurate readings when used repeatedly or if not stored properly. This is because pH meters use the voltage between two electrodes to determine the pH of a solution. The electrodes will not give consistent results if the meter is used repeatedly or the probes containing the electrodes are not stored properly or kept clean. Refrigeration is not a good idea (A) because samples should be tested at standard temperature and pressure since temperature affects pH. Filtering organic matter from a sample (C) is also not necessary and may introduce error. A pH meter does not need to warm up (D) because as soon as it is turned on it records the voltage between the two electrodes.
