Why midday sun can be seen overhead in Chennai twice a year but not even once in Delhi?

The sun can be overhead twice in a year in Chennai because of its geographical position.

i. It lies in the subtropical zone. The subtropical zone is the zone below the Tropic of cancer.

ii. Sun is directly overhead all the places between tropic of cancer and tropic of Capricorn as it constantly moves between them.

iii. At all the places in the subtropical zone, the sun is seen overhead twice a year on the day of the equinox.

iv. An equinox occurs when the duration of day and night is equal. There are two equinoxes every year.

v. At the noon of the equinox, the sun is seen overhead directly in the subtropical zone.