Question

Which of the following is the shortest day in the southern hemisphere?
1. March 21
2. June 21
3. September 22
4. September 23

Answer 1

Hint: The shorter day solstice or winter solstice is the time when the duration of day is shorter in a hemisphere. This phenomenon is opposite in northern and southern hemispheres.

Complete answer:
The solstice is the day when the sun reaches its maximum or minimum declination, marked by the longest and shortest days respectively. They are opposite in nature on either side of the equator, that is to say, what is a summer solstice in the Northern Hemisphere becomes the winter solstice in the Southern Hemisphere, and vice versa. Two solstices occur annually, one on (or around) June 21 and other on (or around) December 21.
Going by the options we can easily make out what is the answer;
1. March 21 is an equinox day or the day when the sun is directly over the equator while a solstice means the distance of sun (inclination towards or away) from a hemisphere which occurs once in 6 months or twice every year in June and December. Thus, the answer is incorrect.

2. This is the correct answer. June 21 is a solstice day or the time when the sun is directly inclined towards the northern hemisphere which results in a longer day and inclined away from the southern hemisphere which gives a shorter day.

3. It is a wrong choice. September 22^nd or 23^rd is the second equinox day when the sun is directly over the equator, unlike the solstice which is the uneven inclination of the sun towards the earth.

4. As stated earlier, September 23^rd is considered as the equinox day and not the solstice day. Therefore, this option is wrong.
Therefore the answer is 2. June 21

Additional Information
An equinox is the day of a year when the plane of Earth's equator passes through the geometric center of the Sun's disk. More simply put, it is the time when the center of the visible Sun is directly above the equator. Such a day occurs twice each year; around 20 March and 23 September.
Note:
 Solstice days occur exactly at the gap of 6 months from the beginning of each year- June and December. They are marked by the sun being directly over the equator. The seasons are reversed in the southern and northern hemispheres because of this phenomenon only; the sun is farther from the southern zone during the first half of each year while closer to it during the latter half and the extreme most points being the solstice days.