The correct answer is: a) Under duress.
The merger of Manipur into India in 1949 was a controversial event that is still debated today. Some people believe that the merger was done under duress, while others believe that it was done with popular support.
Those who believe that the merger was done under duress point to the fact that the Manipuri king, Maharaja Bodhchandra Singh, was forced to sign the merger agreement at gunpoint. They also point to the fact that the merger was not approved by the Manipuri people in a referendum.
Those who believe that the merger was done with popular support point to the fact that the Manipuri people had been demanding independence from British rule for many years. They also point to the fact that the merger agreement was signed by the Maharaja and the Indian government, which they believe represents the will of the Manipuri people.
The truth is that the merger of Manipur into India was a complex event with no easy answers. It is likely that both duress and popular support played a role in the decision to merge.
Option b) is incorrect because there is no evidence that the merger of Manipur into India was done with popular support.
Option c) is incorrect because there was no referendum held on the merger of Manipur into India.
Option d) is incorrect because the merger of Manipur into India was not done through a treaty with the British.