The correct answer is option 4, Indian Independence Act.

The Indian Independence Act of 1947 was passed by the British Parliament, which officially brought an end to British colonial rule in India. This act divided British India into two separate dominions: India and Pakistan.

Option 1, Simla Conference, is incorrect. The Simla Conference was held in 1945 and was a meeting between the Indian National Congress and the Muslim League to discuss the political situation in India. It did not result in the creation of independent states.

Option 2, Cripps proposal, is also incorrect. The Cripps proposal was put forward by Sir Stafford Cripps in 1942 as a plan for Indian constitutional reform. It did not involve the creation of independent states.

Option 3, Cabinet Mission Plan, is likewise incorrect. The Cabinet Mission Plan was a plan proposed by the British Cabinet Mission in 1946 for the transfer of power and the creation of a united India with a federal structure. It did not lead to the creation of independent states.

Therefore, the Indian Independence Act is the correct answer as it directly led to the creation of two independent states, India and Pakistan.