Which of the following longitudes is know as “standard Meridian” in India?

The answer is D) 82°30' E. This is the Standard Meridian of India, the reference longitude on which Indian Standard Time (IST) is based. It runs near Mirzapur in Uttar Pradesh and lies 5 hours 30 minutes ahead of GMT, so IST is GMT + 5:30.

The core concept is that a country's standard meridian is chosen to give one uniform time across a very wide east-west spread, and India is about 30 degrees wide. Choosing a central meridian keeps the time difference between the eastern and western ends of the country manageable. This is a useful Geography point for Mains answers on regional disparity in daylight and work hours in the northeast.

• A) 87°30' E is not the standard meridian. It is a longitude passing through eastern India and is not the reference for IST.
• B) 85°30' E is likewise not the standard meridian and carries no such status.
• C) 84°30' E is also wrong. It is a different longitude, not the reference for national time.

Trap: many aspirants pick the longitude that passes through a familiar city or the one nearest to their home state, or they confuse it with the Greenwich meridian (0°). Remember the fixed fact: 82°30' E, IST = GMT + 5:30.