Indian Standard Time refers to local time of which one of the following places in India?

Indian Standard Time (IST) is calculated based on the 82.5° E longitude, which serves as the Standard Meridian of India [3]. This meridian passes close to the east of Prayagraj, formerly known as Allahabad, in the state of Uttar Pradesh [1]. Specifically, the reference point is often identified as the clock tower in Mirzapur, which is located near Allahabad [t1][t4]. The selection of 82°30' E as the standard meridian ensures a uniform time across the country, balancing the nearly two-hour time lag between India's easternmost and westernmost points [c2][t2]. Consequently, IST is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT) [c1][c4]. While other cities like Bhopal, Delhi, and Lucknow have their own local solar times based on their specific longitudes, they all follow the official time derived from the Allahabad/Mirzapur reference meridian [c2][t8].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 18: Latitudes and Longitudes > Indian Standard Time > p. 245
2. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 18: Latitudes and Longitudes > Standard Time and Time Zones > p. 243