On which of the following pairs of dates is the length of day and night equal on the earth's surface?

The length of day and night is not equal on any of the dates given in the options. On June 21st, also known as the summer solstice, the Northern Hemisphere experiences its longest day of the year and shortest night, while the Southern Hemisphere experiences its shortest day and longest night. On September 21st, also known as the fall equinox, the length of day and night are roughly equal, but not exactly equal. On March 22nd, also known as the spring equinox, the length of day and night are again roughly equal, but not exactly equal. On December 22nd, also known as the winter solstice, the Northern Hemisphere experiences its shortest day of the year and longest night, while the Southern Hemisphere experiences its longest day and shortest night. Therefore, the only option left is March 22nd and September 21st, and while the length of day and night are not exactly equal on these dates, they are very close to being equal, with the difference being only a few minutes. These dates are known as the spring and fall equinoxes, respectively.