Explanation:
When the sun is directly above the equator, it creates a line that divides the Earth into two equal parts. This is known as the equinox. During the equinox, the days and nights are equal throughout the globe.

Reasons:
This happens because of the following reasons:

1. Angle of Incidence: When the sun is directly above the equator, the angle of incidence of the sun's rays is perpendicular to the Earth's surface. This means that the sunlight is falling directly on the equator, creating equal amounts of daylight and darkness.

2. Earth's Rotation: The Earth rotates on its axis, which creates the cycle of day and night. During the equinox, the Earth's axis is perpendicular to the sun's rays, which means that the daylight and darkness are spread equally across the globe.

Other Options:
The other options in the question are incorrect because:

A) Poles: The poles experience periods of complete darkness and complete daylight, depending on the season.

C) Tropic of Cancer: The Tropic of Cancer is located at 23.5 degrees north of the equator. When the sun is directly above the Tropic of Cancer, it is the summer solstice in the northern hemisphere and the winter solstice in the southern hemisphere. This means that the daylight and darkness are not equal across the globe.

D) Tropic of Capricorn: The Tropic of Capricorn is located at 23.5 degrees south of the equator. When the sun is directly above the Tropic of Capricorn, it is the winter solstice in the northern hemisphere and the summer solstice in the southern hemisphere. This means that the daylight and darkness are not equal across the globe.