The correct answer is option 4: Polar.

Insolation refers to the amount of solar radiation received on the Earth`s surface. The seasonal contrast of insolation refers to the variation in the amount of solar radiation received during different seasons.

In polar regions, such as the North and South Poles, there is a significant seasonal contrast of insolation. During the summer months, the poles receive 24 hours of daylight, resulting in continuous sunlight. This is known as the midnight sun phenomenon. In contrast, during the winter months, the poles experience 24 hours of darkness, with no direct sunlight at all.

On the other hand, the equatorial zone (option 1) experiences fairly consistent insolation throughout the year, with only minor seasonal variations. The tropical zone (option 2) also has relatively consistent insolation, with slight variations due to the changing position of the sun between the Tropic of Cancer and the Tropic of Capricorn. The temperate zone (option 3) experiences moderate seasonal variations in insolation.

Therefore, the greatest seasonal contrast of insolation occurs in the polar regions, making option 4 the correct answer.