Question

what do we need a standard meridian where it is located what it is located what its singnificance

Answer 1

since Indian is a very large country, it needs a uniformity in time. 

If their will different times at different places, then it would be a lot confusing. Hence to remove this confusion, the Meridian 82'30 Degrees passing near Allahabad is taken as the standard meridian.

The significance of standard meridian of India is that Standard meridian is used as the standard time for whole country.