When the GST reform was rolled out through the 101st Constitutional Amendment Act, 2016, three separate new Articles were added to handle three separate jobs. Article 246A gave Parliament and the states the concurrent power to actually make GST laws. Article 269A dealt with how tax collected on inter-state supplies gets divided between the Union and the states. Article 279A created the institution that would recommend rates, exemptions, thresholds and other GST rules on an ongoing basis, since a tax shared between the Centre and so many states needs a standing body to keep rates uniform and resolve disagreements.
That standing body is the GST Council, and Article 279A spells out its membership: the Union Finance Minister chairs it, joined by the Union Minister of State for Finance and one nominated minister from each state government, usually the state Finance Minister. Decisions are taken by a weighted vote, with the Union having one-third of the votes and all states together holding two-thirds.
Article 263 is an older, general-purpose Inter-State Council for broader Centre-state disputes, unrelated to GST specifically, and Article 281 is about the Finance Commission's reports, a different fiscal body altogether.
The correct answer is Article 279-A, the specific provision that constitutes the GST Council.