If a diver completes a dive to 17 metres for 47 minutes, what should they do after realizing they have exceeded their bottom time on a second dive?

When a diver realizes they have exceeded their bottom time on a second dive, the appropriate action is to ascend to a depth of 5 meters and remain there for a safety stop. This practice helps in off-gassing any excess nitrogen absorbed during the dive. During moderate-depth dives, exceeding planned bottom times increases the risk of decompression sickness due to the accumulation of nitrogen in the body.

By ascending to 5 meters and staying for the recommended duration, the diver allows their body to safely off-gas nitrogen before returning to the surface, which greatly reduces the chances of experiencing any diving-related health issues. This step is crucial for diver safety and follows standard diving practices that are taught in diver training courses, such as those provided in the PADI Open Water Diver program.

The other options may not adequately address safety. Ascending immediately to the surface could increase the risk of decompression sickness without allowing sufficient time for nitrogen to be off-gassed. Continuing to dive for additional time further endangers the diver's safety by allowing even more nitrogen absorption. Terminating the dive and returning to the boat does not include the critical safety stop, which serves as an essential precaution in the diving procedure.