Question

what are amendment .why is it necessary

Answer 1

a minor change or addition designed to improve a text, piece of legislation, etc. The first ten amendments to the Constitution are collectively known as the Bill of Rights. These amendmentsare important because they protect some of our most important freedoms. ... The First Amendment is extremelyimportant as it protects our rights to self-expression.
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Answer 2

The Constitution provides for clear division of powers in respect of taxation between the Centre and states. While the Centre at present does not have the right to tax sale of goods, except in the case of inter-state sale, states cannot levy tax on services.

The divisions are mentioned in the Article 246 under the Seventh Schedule of the Constitution. The Constitution needs to be amended to provide for giving power to both the Centre and states in respect of GST, a single tax on goods and services.

Therefore, the very first provision of the Bill is to add Article 246A after Article 246.

It says Parliament and the legislature of every state will have the power to make laws with respect to goods and services tax imposed by the Union or by such state.

In the case of inter-state supply of goods or services or both, only Parliament will have the power......

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