A single vertical magnet placed underneath the compass in the binnacle is used to compensate for __________.

Correct Answer: Option B — deviation caused by the vessel's inclination from the vertical

A heeling magnet, positioned vertically under the compass, compensates for deviation induced when the vessel heels. As the ship tilts, the vertical component of the ship's magnetism and the vertical soft iron magnetism shift relative to the compass card, creating an error that this magnet is specifically designed to neutralize.