Question

what is IST why have we taken one time zone for whole India​

Answer 1

Answer:

IST is Indian standard time

Explanation:

What's unusual is that there is only one time zone across the whole of India. The time zone is calculated according to the longitude of 82.5° E. at Shankargarh Fort in Mirzapur (in the Allahabad district of Uttar Pradesh), which was picked as the central meridian for India. It's also important to note is that Daylight Saving Time doesn't operate in India.

Answer 2

local time that prevails on that longitude is taken as the standard time for the world country this is called Indian standard time or IST