B.R. Ambedkar, a key figure in drafting the Constitution of India, was elected to the Constituent Assembly from West Bengal. Let`s understand each option:

Option 1: West Bengal - This is the correct answer. Although Ambedkar lost the election in Bombay (Mumbai, which is in option 2) to his Congress opponent, he was taken to the Constituent Assembly from West Bengal, where the Scheduled Castes had gained in strength.

Option 2: Bombay Presidency - This is not correct as Ambedkar lost the election from the Bombay Presidency but was, later, included in the Constituent Assembly from West Bengal.

Option 3: The then Madhya Bharat - This option is incorrect. Madhya Bharat was a region in Central India, appearing much later, and Dr. Ambedkar had no significant electoral connection with this region.

Option 4: Punjab - This option is incorrect. Despite being a major state, Dr. Ambedkar had not been elected from Punjab. His significant political and electoral engagements were primarily with West Bengal and Bombay presidency.