Option 1: The International Date Line is largely based on the 180° meridian. This statement is correct. The International Date Line is approximately based on the 180° meridian, with some deviations to avoid splitting countries and land masses.

Option 2: The difference in time between the places just either side of the International Date Line is almost one day. This statement is correct. When crossing the International Date Line from east to west, you lose a day, and when crossing from west to east, you gain a day.

Option 3: The difference in time to the extent of one day on either side of the International Date Line is caused by the inclined axis of the Earth. This statement is incorrect. The difference in time on either side of the International Date Line is not caused by the inclined axis of the Earth. It is primarily due to the need for consistent calendars and timekeeping across different regions.

Option 4: The International Date Line mostly passes through the Pacific Ocean. This statement is correct. The International Date Line runs primarily through the Pacific Ocean, although it deviates at some points to accommodate political boundaries.