The correct answer is option 1, Allahabad. Indian Standard Time (IST) refers to the local time of Allahabad. IST is the time standard used throughout India and is five and a half hours ahead of Coordinated Universal Time (UTC+5:30). It is the time followed by the entire country, including major cities like Delhi, Mumbai, Kolkata, and Chennai.
Option 2, Bhopal, is not the correct answer. Although Bhopal is a city in India, it does not determine Indian Standard Time.
Option 3, Delhi, is also not the correct answer. Delhi is a major city in India, but it does not determine Indian Standard Time. However, Delhi does follow Indian Standard Time, just like the rest of the country.
Option 4, Lucknow, is also not the correct answer. Lucknow is a city in India, but it does not determine Indian Standard Time.
Indian Standard Time is determined based on the longitude of Allahabad, which is approximately 81.8 degrees East. This reference point helps synchronize time across the entire country.