How much is the difference between Indian Standard Time (I.S.T.) and Greenwich Mean Time (G.M.T.)?

Which one of the following countries has the maximum time difference from Greenwich Mean Time (GMT) ?

The Indian Standard Time Meridian does not pass through

The basis of deciding the standard time of any place is–

How many hours of time difference will be there between the most western village of Gujarat and the most eastern village of Arunachal Pradesh, Walong?

If the difference of longitudes for the two places is 90°, the time interval between these places will be –