Final answer:
A non-grounded GFCI outlet will trip when the test button is used but may not trip with an external tester. The GFCI works by detecting current imbalances and trips at a leakage current greater than 5 mA.
Step-by-step explanation:
When testing a GFCI outlet that is not grounded, the outlet will typically trip with the test button on the outlet, but not by the tester, as per option B. This is because a GFCI, or ground fault circuit interrupter, functions based on electromagnetic induction, comparing currents in the live/hot and neutral wires. When it detects an imbalance, such as a leakage current greater than 5 mA indicating that some current is finding an alternative path which could be hazardous, the GFCI will trip to interrupt the circuit. However, conventional testers rely on a grounding connection to measure the fault and may not function properly if the outlet is not grounded. Hence the test button, which does not require the outlet to be grounded, will trip the GFCI, forcing a repair of the leakage, while an external tester might not.