Concept:Equinox occurs when the Sun is directly above the equator, making day and night nearly equal in length.
Explanation:There are two equinoxes each year.
The vernal (spring) equinox falls on 21st March.
The autumnal (fall) equinox falls on 23rd September.
These dates are the same worldwide, including India.
Equinox is the moment the Sun crosses the celestial equator.
21st June and 22nd December are solstices, not equinoxes.
Therefore, the correct pair is 21st March and 23rd September.
Answer:D. 21st March and 23rd September