ऋग्वेद में सर्वाधिक सूक्त/मंत्र किस देवता की स्तुति में समर्पित हैं?

In Ancient Indian Statecraft, Kautilya's 'Rajamandala' theory primarily deals with:

The First Buddhist Council was held at ______.

Which ancient Indian text contains references indicating that population counts or census-like records were maintained in ancient India?