If India were to adopt two time zones based on the 75° E meridian for western India and the 90° E meridian for eastern India, the state of Manipur in eastern India would be the one to benefit the most.
To understand why Manipur would be the most benefited, we need to consider the geographical location of the state in relation to the proposed time zones. Manipur is located towards the easternmost part of India, closer to the 90° E meridian. By adopting the time zone based on this meridian, Manipur`s local time would be more aligned with its actual solar time. This means that the sunrise and sunset timings in Manipur would better correspond to the actual daylight hours in the region.
On the other hand, the other states mentioned in the options - West Bengal, Assam, and Bihar - would be located closer to the western time zone based on the 75° E meridian. This would result in a greater difference between their local time and actual solar time, which could potentially lead to issues such as longer dark hours in the mornings or evenings.
Therefore, considering the geographical positioning, Manipur would see the greatest benefit from adopting the time zone based on the 90° E meridian.