The correct answer is option 2: GST was to be implemented on a concurrent basis and Article 246 was inadequate for such a case.

GST is a tax reform that seeks to unify India`s indirect taxation system by subsuming various taxes such as excise duty, service tax, and value-added tax. Implementing GST required constitutional amendments because the power to tax and collect revenues is distributed between the central government and the state governments under the Indian Constitution.

Option 1, which suggests that states were not willing to agree with the Union for the introduction of GST without amending the Constitution, is not an accurate explanation. While states may have had concerns about GST implementation, the need for a constitutional amendment was primarily due to the structure of the tax itself.

Option 3, stating that the Empowered Committee of Finance Ministers recommended a constitutional amendment, is not necessary to explain the need for an amendment. The recommendation of the committee does not inherently require a constitutional amendment.

Option 4, suggesting that the GST Council recommended a constitutional amendment to enhance its power, is an inaccurate explanation. The GST Council was formed to make decisions related to GST implementation but did not have the power to recommend constitutional amendments.

Therefore, option 2 remains the most accurate explanation for why a constitutional amendment was needed