Question

why it is still dark in Gujarat the sun has already rise in Arunachal Pradesh? Give any reason in support of this answer

Answer 1

it is because of the standard time which is taken along the standard meridian

Answer 2

The Earth is spherical (or oblate) in shape Therefore it experiences sunrise and sunset in various places with different time.
Gujarat being in west and Arunachal Pradesh in the opposie side,they have different times for their sunrise and sunset this is because of the rotation of the Earth.
Hope it helps..