Final answer:
The correct amount of time to wait before reading the pH paper results for gastric contents is 30 seconds, as this allows for accurate assessment and avoids false-negative or false-positive readings.
Step-by-step explanation:
When using pH paper to test gastric contents, it is important to wait the correct amount of time before reading the results to ensure accuracy. In the context of testing with pH strips or similar test strips, it's mentioned that a typical glucose test strip used with urine requires approximately 30 seconds for the completion of the color-forming reactions. Based on the provided reference and analogous procedures, it can be assumed that the appropriate time to wait before reading the pH paper results for gastric contents is similarly 30 seconds (Option C). Reading the results too soon may lead to a false-negative result, while waiting too long may result in a false-positive due to other reactions.