The Montague-Chelmsford Report formed the basis of:

The Government of India Act, 1919.

The Montague-Chelmsford Report, also known as the Montagu-Chelmsford Reforms, was a significant British constitutional proposal for India. It was published in 1918 and formed the basis for the Government of India Act of 1919. The Act introduced several reforms, including the expansion of legislative councils, the introduction of dyarchy (separation of powers) in some provinces, and the provision for limited franchise.

Therefore, the correct answer is: The Government of India Act, 1919.