The most critical part of the bunkering operations, which can result in an oil spill, is when the __________.

Correct Answer: Option B — tanks are being topped off

Topping off is the most critical phase of bunkering because the ullage space is rapidly decreasing, leaving little margin for error. A slight delay in closing valves or a surge in flow can lead to an immediate overflow through the air vents, resulting in a significant environmental spill.