Under the IALA cardinal system, a mark with quick white light showing 3 flashes every 10 seconds indicates that the safest water in the area is on the __________.

Correct Answer: Option B — east side of the mark

IALA Cardinal marks utilize light characteristics to indicate safe water. An East Cardinal mark displays a quick or very quick white light with three flashes, corresponding to the mnemonic 'three o'clock' on a clock face. This signifies that the safest water lies to the east of the mark.