The International Date Line represents the point where the date changes as one travels across it. It is important for maintaining standard time and synchronizing dates across different regions of the world.

Option 1: The 100° meridian is not the International Date Line. Meridians are lines of longitude that run from the North Pole to the South Pole and are used for measuring coordinates on the Earth`s surface. While the 100° meridian is significant for other purposes, it is not associated with the International Date Line.

Option 2: The 0° meridian, also known as the Prime Meridian, runs through Greenwich, London, and is used as the reference point for measuring longitude. While it is significant for determining time zones, it is not the International Date Line.

Option 3: The correct answer is 180° meridian. The International Date Line roughly follows the 180° meridian of longitude. When crossing the International Date Line from east to west, the date is advanced by one day. It is an imaginary line that does not follow the exact meridian due to political and geographical considerations.

Option 4: The 90° meridian does not represent the International Date Line.