Inaccurate calibration of the pH probe leads to which type of error?

• A. Random error
• B. Instrumental error
• C. Systematic error
• D. Methodological error

Answer: (B)

Inaccurate calibration introduces a bias from the measuring instrument itself. A pH probe that isn’t calibrated correctly will give readings that are consistently offset from the true value, regardless of the sample. That constant offset is a hallmark of instrumental error, arising from the device’s own limitations or faults. It’s different from random error, which would scatter results unpredictably, and from methodological errors, which come from the procedure rather than the instrument. With a miscalibrated instrument, the bias makes all measurements systematically wrong, which is why this is categorized as instrumental error.