The correct answer is option 1: "to permit certain land areas and groups of islands to have the same calendar day".

The International Date Line is an imaginary line that is drawn on the Earth`s surface, mostly following the 180th meridian. Its purpose is to establish where one calendar day ends and the next begins.

Option 1 correctly states that the zigzag pattern of the International Date Line allows for certain land areas and groups of islands to share the same calendar day. This is done in order to avoid situations where neighboring regions have different dates, which could create confusion in terms of scheduling and communication.

Option 2, which suggests that the zigzag pattern facilitates sailors in adjusting the time on their watches, is not accurate. The purpose of the International Date Line is mainly related to maintaining consistency in calendar dates, rather than adjusting individual timepieces.

Option 3, which mentions adjusting the day in the calendar while sailing from east to west and vice versa, is not a primary reason for the zigzag pattern of the International Date Line. The primary purpose is to establish consistent calendar days for specific regions.

Option 4 suggests that the zigzag pattern is meant to make the 180°E and 180°W meridians coincide. This is not accurate