Question

why there is a 2 hours time lag between Gujrat and Arunachal Pradesh

Answer 1

because the longitudinal extent of india there is a difference of 30 degree from west to east india.

Answer 2

$\huge\underline\mathfrak\color{blue}Answer$

Beacuse they both lie on different longitudes. ... The time along the Central Meridian of India i.e. 82 32' E passing through Mirzapur (in Uttar Pradesh) is taken as the standard time for the whole country.