Explanation : Indian Standard Time is calculated on the basis of 82.5° E longitude, from a clock tower in Mirzapur (25.15°N 82.58°E) (near Allahabad in the state of Uttar Pradesh) which is nearly on the corresponding longitude reference line.
A. 81° East longitude – Incorrect. Close, but not the standard reference. B. 82.5° East longitude – Correct. Official meridian for IST. C. 84° East longitude – Incorrect. Lies further east. D. 86° East longitude – Incorrect. Even further east than 84°.