Answer : 2. "1st July 2017"
Explanation :

1. The 101st Constitutional Amendment of 2016 is the most far-reaching change from a fiscal perspective since the formation of the first Finance Commission in 1951, providing concurrent powers to the Center and the states in the matter of indirect taxation.

2. This amendment introduced a national Goods and Services Tax (GST) in India from 1 July 2017.

3. GST is based on a concurrent system of indirect taxes, where central and state GST is imposed on every transaction.