What color and shape of buoys are marked with odd numbers?

The correct answer identifies that odd-numbered buoys are marked with green and are typically cylindrical in shape. In the United States, the marking system for navigational aids follows the IALA (International Association of Lighthouse Authorities) standards. According to these standards, odd-numbered buoys are green and signify the port side for vessels returning from sea or upstream on a river. The color green helps distinguish these buoys from red ones, which indicate safe passage or navigation channels for vessels. The cylindrical shape is also specific to these buoys, allowing for easy identification on the water.

In contrast, the other options do not align with the established navigational buoy color coding:

• Red and cone-shaped would represent even-numbered buoys, indicating the starboard side.
• Blue and rectangular are typically used for informational buoys and do not follow the numerical marking system.
• White and flat buoys do not correspond to any specific numbered markings in the standard buoyage system.